As the title says, what is the weirdest "instrument" you made use of during either making sound effects or soundtrack/tune/songs in game.
This might not be the weirdest, but one of the most fun times I had involved bringing my bassoon into the studio to record. We attached a pipe to the bell of the instrument, attached that tube to another tube, and put a rubber doctor's glove at the end. It involved three people, not including me, to keep the contraption all together! And the sound was a pretty satisfying low fog horn type thing- I wish I could play that note without needing all the extra equipment!
I also brought my cockatiel in once- we haven't used his tweets for anything yet as far as I'm aware, but I hope he gets in there at some point!
Ha! I've actually done the rubber-glove-on-the-end-of-my-bassoon trick.
EU Gunner's Hold
The rest of the audio team has probably used weirder stuff than I have (so far), since most of my work uses traditional orchestral instruments. However, on the piece called "Maws of the Ruptured Heart" on PoF, the main melody is being played on a bass flute, which is pretty unusual for an orchestra.
Mixed into the track are some sounds that the flautist did after we recorded her main part. She would make a sort of Chewbacca growl into the flute while playing a note, and then she would change the pitch of the growl while maintaining the flute note, and it would create all of these crazy overtones and wild alien sounds. It was something I didn't know was possible, and I ended up taking them, cutting them up, and putting a ton of effects and reverb on them to create a background layer that no synthesizer could replicate. Pretty cool.