I refer of course to money.

The Economics of Stripping. According to researchers at University of New Mexico strippers make more money when they're ovulating, because it's at the time when men find them most attractive: "Surprisingly, Miller found that strippers who were in the estrus phase made $354 per shift compared to $90 during the luteal phase and $170 more than during the menstrual phase. The use of birth-control pills didn't help results, with woman on oral contraception earning about $80 less per shift."