You forgot cajones, Gyrene.
Actually tuercas is correct...cajones is slang for balls but the correct spelling would be cojones which changes the definition:
Plural for "cajon", spanish for drawer, but also is an peruvian instrument that resembles a big wooden box, the player sits on it an then hit it in the frontal face to create diferent sounds depending on how and where he/she hits it.
If you really wanted to say balls in Spanish it would be bolas.