man this film still creeps me out.
here's the info I was thinking about, curteousy of IMDB

When the shark attacks Hooper's cage, there's live footage of a real Great White with a rope hanging from its mouth. This shark's mouth is clearly much smaller than the shark's mouth when it attacks the boat moments later. These scenes were filmed by noted shark photographers Ron Taylor and Valerie Taylor specifically for the movie. Because the Great White sharks they filmed would be smaller than the mechanical shark in the movie, they constructed a smaller version of Hooper's shark cage. Inside the cage they alternately used a small mannequin or a little person. One of the sharks they attracted got caught in the cage's cables and tore it apart trying to escape. The footage was so good that they changed the script to reflect the destroyed cage and Hooper escaping by hiding on the ocean floor. However, the small person used in the scene refused to go back in the miniature cage, which was damaged in the incident.

From Wiki:

The song's title character is a transvestite whose primary pastime is stealing women's clothes and undergarments from washing lines. Some believe that "Arnold Layne" was actually based on a real person, and that he routinely stole underwear from the mothers of Barrett and bassist Roger Waters during their childhood days in Cambridge.

However, despite finding a place in the Top 20, the song's unusual transvestism theme attracted the ire of Radio London, which deemed the song too far-removed from "normal" society for its listeners before eventually banning it from radio airplay altogether.

Producer Norman Smith wanted the band to re-record the Joe Boyd-produced song after they had signed up with EMI. While Waters and keyboardist Richard Wright were willing to do this, Barrett, on the other hand, was entirely satisfied with the existing studio cut, and argued against recording another version.

A black and white promotional film of "Arnold Layne" was made the same year, and featured members of Pink Floyd dressing up a mannequin before showing it around a beach. Recently, an alternative promotional film was unearthed, which featured the young Floyd goofing around in a forest and in front of a church. It is also the only known footage of Syd Barrett lip synching to the song.

This happened when I was in high school.

On a side note . . . friends of mine told tales of some local Tulane fraternities that had Jonestown parties. My friends talked about mannequins strewn around and a big bowl (I guess) of purple Kool-Aid. That’s college humor for ya . . .

i went to see the movie version a couple of years ago in tokyo. at the theater, all the mannequins of the fuccon family were standing to welcome the customers. i took some photos with them. that was wonderful.

OH NO! Guns are so nasty and evil. In fact, why doesnt the government ban gun ownership like the UK did? Oh yeah, that annoying Constitution thing. Damn it, always getting in the way. Well, enjoy the video about the mannequin getting its lungs punctured by that nasty AK-47. Also, it argues that its apparently too easy to use and is to blame for child soldiers around the world. Arms running will always exist and signing a treaty will not fix the already illegal arms trade. Of coure Amnesty International should be declared an enemy of the U.S. and destroyed like the rest of the terrorists they support. Who knows how many U.S. soldiers they have gotten killed.