The 
Guinea Pig films (from the Japanese 
"giniipiggu") are a series of 
1980s Japanese horror films with extremely detailed 
special effects. According to 
Snopes, the films became infamous when 
Charlie Sheen mistook one for a 
snuff film and contacted the 
FBI to report it.
[1] The tapes gained notoriety in the late 1980s and early 1990s when the first five films of the series were found showcased in the 5,763 videotape collection of Japanese 
serial killer Tsutomu Miyazaki, who re-enacted scenes from the films as a part of his crimes.