Quote from Phoebe in The One Where Rachel Finds Out
Joey: It's a fertility study. Monica: Joey, please tell me you're only donating your time. Joey: Come on, you guys, it's not that big a deal. I just go down there every other day and make my contribution to the project. But at the end of two weeks, I get $700! Phoebe: Wow. You're gonna be making money hand over fist.