Cowboy BeBop at His Computer: Due to the film being created by Nick Park and, therefore, sporting his design style, some American viewers viewing the original short (or parts thereof) mistook it for an existing or forthcoming Wallace & Gromit short where said characters visit the zoo.
Development Gag: Some little quirks about the interviewees made it into the animations. One interviewee was a man who was always getting called away in the middle of his sessions, so the animators made him a greyhound who's race always begins mid-interview.
Throw It In: The entire point of the films. Nothing is scripted, all of the interviews are 100% authentic and all of the art and animation are done long after they've been edited down to a reasonable running time.