I think I remember my father telling me about a cat who wandered into a particle collider as it was being built. It died inside, and nobody realized it until they tried to pump it down to a vacuum - and kept failing, because the dead animal kept outgassing.

I can't find any corroborating evidence after a 5 minute google search, so it might be an urban legend - but regardless, the answer to the next-to-last question is pretty well known.