Contractions

So I've gotten the generalized "you will know when you're having one" answer to my question about 100 times, but I'm just curious what everyone's experience with contractions has been. I've talked to a couple people who have said that they were comparable to severe period cramps and a couple others says they feel like (TMI warning) pains you get when you're having diarrhea or throwing up. What were yours like?