I was listening to Episode 57 of the Talk Show (at 44:35), and one of the hosts mentioned that he'd heard that slot machines all play in the key of C. Ostensibly, this is because this frequency is especially pleasing.
The show notes linked to an ask.metafilter page with worthless posts that provide none of the research that makes for a good answer here on Skeptics.
Is there evidence that slot machines play in the same key?
If so, is some sort of path dependent artifact or is there a reason C was actively chosen?