The Human Centipede is a series of three horror films written and directed by Dutch filmmaker Tom Six, in which various madmen surgically attach their victims mouth-to-anus in order to construct what is known as a 'human centipede'.

The first film in the trilogy, The Human Centipede (First Sequence), was submitted to the BBFC in June 2010, initially for DVD release only, with a request for an 18 certificate from the distributor. It follows two young American tourists, Lindsay and Jenny, on a trip through Europe. When their car gets a flat tyre, they are forced to seek shelter in the home of a retired surgeon, Dr Josef Heiter, who secretly plans to transform the two women and a third captive, a Japanese man named Katsuro, into the world's first 'human centipede'.

By the time the film arrived at the BBFC it had already enjoyed a theatrical release in the US and been screened at many international film festivals, including London's FrightFest, attracting some press attention for its outlandish central conceit. Two Examiners viewed the film, and concluded that the key issues of strong bloody violence, threat and horror were suitably placed at the requested 18. Additional issues including strong language, sex references and non-sexualised female nudity were also noted.

Scenes of violence include depictions of the surgical procedure by which Heiter creates his 'centipede'. For example, in one scene, he uses pliers to remove a tooth from one of his female victims, resulting in significant bloodshed. In another, a scalpel is seen cutting into the flesh of a woman's buttocks and a flap of bloody skin being lifted. There are also a bloody shooting and a scene in which a character cuts his own throat with a shard of glass. The BBFC Classification Guidelines state that while violence may be strong at 15, it should not dwell on the infliction of pain or injury and that strong sadistic violence is unlikely to be acceptable. Both Examiners agreed that the violence in The Human Centipede (First Sequence) exceeded these tests, though it was noted that the film's violence fell short of other recent 18-rated horrors, like the Saw and Hostel films, both in terms of gory detail and sadistic relish.

Scenes of horror and threat see Heiter's three victims chained up, drugged and terrorised by his explanations of what he plans to do to them. Like the violence, these were thought too much for 15 – where a sustained focus on sadistic threat is unlikely to be acceptable – but quite comfortably placed at the adult category.

Finally, The Human Centipede (First Sequence) contains a scene in which Katsuo, positioned at the front of the 'centipede', is implied to be defecating into Lindsay's mouth, which is attached to his anus. In regards to this sequence, the BBFC sought legal advice to confirm that the film was not in breach of the Obscene Publications Act 1959 (OPA). While it was acknowledged that the concept of a 'human centipede' and the scatological implications thereof had potential to cause significant disgust and offence, the film's depiction of this concept was deemed unlikely to be considered obscene under the terms of the OPA, which requires that a film be considered as a whole, rather than on the basis of individual scenes. The film was accordingly passed 18 uncut – a decision that was upheld when it was subsequently submitted for theatrical release.

Writer/director Tom Six announced plans for a second Human Centipede film shortly after the release of the first, and stated his aim to make the sequel even more extreme and disturbing. The resulting film, The Human Centipede 2 (Full Sequence), was submitted to the BBFC for DVD release in April 2011, on an advice viewing basis. Once again, an 18 certificate was requested.

The narrative follows Martin, a disturbed car park attendant who is sexually obsessed with the first Human Centipede film. As his mental state deteriorates, Martin becomes inspired to re-enact the film and create a twelve person 'human centipede' of his own. During the film Martin abducts, tortures, mutilates, sexually assaults and murders his victims, all of which is depicted in graphic detail. For example, in the process of creating his 'centipede' we see him cutting into knees and buttocks, removing teeth with a hammer, stapling lips to buttocks, and feeding his victims laxatives so they are forced to defecate into each other's mouths, an act which is depicted in significantly more detail than in The Human Centipede (First Sequence). After becoming aroused by this, Martin proceeds to wrap barbed wire around his penis and rape the woman at the rear of the 'centipede'. In another sequence, he masturbates using sandpaper while watching the original Human Centipede film. There is also a scene in which a newborn baby is violently killed.

The Human Centipede 2 (Full Sequence) was viewed by the two Senior Examiners, who had concerns about the film's content and referred it to the Director and Presidents for further consideration. The Classification Guidelines clearly set out the BBFC's concerns about any portrayal of sexual violence which endorses or eroticises the behaviour. The BBFC are also obliged under the Video Recordings Act 1984 (VRA) to have special regard to the likelihood of any harm that may be caused to the viewer or, through their behaviour, to society. This risk of harm includes encouraging a dehumanised view of others, callousness towards victims and taking pleasure in the pain and humiliation of others. In The Human Centipede 2 (Full Sequence), it was noted that there is little attempt to portray any of the victims as anything other than objects to be brutalised, degraded and mutilated for Martin's amusement and arousal, as well as for the pleasure of the audience. There is a strong focus throughout on the link between sexual arousal and sexual violence and a clear association between pain, perversity and sexual pleasure; an aspect that was entirely absent from the first Human Centipede film.

After careful consideration, it was judged that to issue a certificate to the uncut version of The Human Centipede 2 (Full Sequence) would involve risk of harm within the terms of the VRA, would be inconsistent with BBFC Guidelines and broad public opinion, and that the film may even be considered obscene within the terms of the OPA. It was also felt that the cuts required to address these issues would be extensive and complex. Accordingly, the company was advised that the film was likely to be refused a classification if submitted formally, which is what happened when this subsequently occurred.

The Human Centipede 2 (Full Sequence) was seen again once the distributor had implemented their own cuts to the film, but it was determined further cuts were required before a certificate could be issued. Ultimately 32 individual cuts were made to scenes of sexual and sexualised violence, sadistic violence and humiliation, and to scenes in which a child is presented in an abusive and violent context. Totalling 2 minutes and 37 seconds, the cuts met the BBFC's requirements and an 18 certificate was finally granted. The same cuts were replicated when the film was submitted for theatrical release, and it was once again classified 18.

The third and final film in the trilogy is The Human Centipede III (Final Sequence), in which a depraved prison warden introduces disciplinary measures inspired by the two previous Human Centipede films, leading to the creation of an enormous five-hundred person 'human centipede'. It was submitted to the BBFC for theatrical release in April 2015, with an 18 request from the distributor.

Considering the controversy surrounding the previous film in the series, The Human Centipede III (Final Sequence) was viewed by the Senior Examiners and Director in addition to the normal complement of two Examiners.

The primary classification issue in The Human Centipede III (Final Sequence) is frequent strong bloody violence and gore, including scenes of torture and mutilation that often dwell on the infliction of pain and injury in a manner that exceeds the Guidelines at 15. For example, one inmate is waterboarded with boiling water and another is castrated. There are also scenes of sexual violence, including brief clips from the previous film's barbed wire rape scene, although nothing that had been cut by the BBFC. Other issues include crude verbal and visual sex references, a brief explicit image, scenes of strong sexual activity, very strong language, and the use of discriminatory language.

However, while it was clear the film could not be passed any lower than 18, it was agreed by the viewing team that no further intervention was required. Unlike the unremittingly grim second film, the third instalment is clearly intended as an exercise in bad taste excess, with a much more overtly comic tone than its predecessor. In an example of its self-referential humour, writer/director Tom Six makes a cameo appearance, playing himself and advising the prison warden on the creation of his 'centipede'. The film's scenes of sexual violence lack any eroticising elements and were not deemed to pose a credible harm risk. While it was acknowledged that The Human Centipede III (Final Sequence) certainly had potential to be shocking and offensive to some viewers (its poster boasts that it is "100% Politically Incorrect") the BBFC saw no grounds to intervene at the adult category and the film was classified 18 uncut.