I know this one is VERY strange.  But yeah, I get very turned on at the thought of a hot girl throwing up. It's weird because I actually have a phobia of myself puking, but for some reason I get aroused when thinking about a girl doing it. Using your finger would certainly be hot, though I am even more turned on if you really felt like you had to puke--it was an involuntary bodily reaction that you could not stop. I also love the anticipation building up to it, as the urge to puke is welling up in your stomach. There could be many ways to effect this naturally--overeating, overindulging in alcohol, certain medications, one girl could just burp a lot to get it going... I know this is a weird one, but we are all weird in our own way, and I'm sure there are some out there who wouldn't find this too difficult.