Q:I am a movie director and I just received the following movie plot. Could you help me answer this question? If not, let me know by writing "Not answerable". Plot title: The Human Centipede Movie plot: Lindsay (Ashley C. Williams) and Jenny (Ashlynn Yennie), two American tourists in Germany, are drugged and involuntarily detained by crazed surgeon Dr. Josef Heiter (Dieter Laser) when they seek help at his house after they get a flat tire. The women awake in a makeshift medical ward. They witness Heiter kill a kidnapped truck driver after Heiter informs him he is "not a match". Heiter secures a new male captive, Japanese tourist Katsuro (Akihiro Kitamura). The doctor explains that he is a world-renowned expert at separating Siamese twins, but dreams of making new creatures by sewing people together. He describes in detail how he will surgically connect his three victims mouth-to-anus, so that they share a single digestive system. After Lindsay tries to escape and fails, Heiter explains that he had previously experimented with creating what he called a "three-dog", also joined mouth-to-anus. However, the three-dog died shortly after surgery. Heiter tells Lindsay that one dog tried to escape and that dog became the middle, thus this caused the most pain to the dog and as punishment for her escape attempt, she will become the middle part of his centipede. Heiter performs the surgery, placing Katsuro at the front, Lindsay in the middle and Jenny at the rear. He removes the front teeth of both women and mutilates the buttocks of both Katsuro and Lindsay in order to provide easier access to the rectums, to which he hideously stitches and grafts their mouths. During his procedure, he severs the ligaments within his victims' knees to prevent leg extension, forcing his victims to crawl. He then connects his victims together in a straight line with their mouths surgically attached to the anus of the victim in front of them. Once the operation is complete, Heiter attempts to train his centipede as a pet, often belittling Katsuro with racist insults and beating him with a crop when he becomes rebellious. When Katsuro defecates, Lindsay is forced to swallow his excrement while the doctor watches in delight. However, he... My question: Dr. Heiter had tried this experiment on what type animal?
A:
Three dogs.