Over two tons of klay - er, clay were used to animate The Neverhood Chronicles. Perhaps, it's the only game in the series to be done in pure clay: according to "the making of" videos (available only at Doo's site, appearantly), Skullmonkeys actually uses latex to save development time... While Boombots and Klaymen Klaymen Gun Hockey don't use any clay for the ingame process at all, because they actually using 3D models.
The radio song "Sound Effects Record #33" contains backmasked singing in the shower. If you reverse it, the song being sung turns out to be "Khumbaya."
The radio song "Chiming In" is also backmasked. The eerie, dissonant sounds are those of a music box, and all the background noises captured while recording it, including someone breathing into a mic and the music box being wound.
Slow down the radio "song" "Scary Robot Man," and its' true nature will be revealed: It's a sped-up, distorted ramble, done in a vaguely Indian/Hindi accent, about... being lost at a wedding, Slurpees, and McDonalds.