it depends who does it and how rough they are... apparently also if you're less favourable it's more sore as well
I had 2 and the first was fine, didn't hurt or anything, but it didn't work.
so 3 days later I had the second. Perhaps it was that she knew the first hadn't worked, but she was really rough and I was so shocked! never felt that sort of pain before as it was sharp pains that radiated right into my groin. It only lasted 30 seconds or so, it might have been agony but it did the trick as I had cramps/contractions straight away that progressed into labour
breathe slowly and deeply if you can, that helps. Next time I'd just ask them to do a rough one straight away :P