Now that surprises me, I would have thoguht that the tongue would hurt more than the belly button considering the amount of nerves and stuff in the tongue and also the fact that it's actually a muscle. Whereas the belly button is just skin.
As I said, my tongue hurt a lot more than my lower lip, mainly due to the fact that the lip is just skin. Mind you, I have odd reactions to anaesthetic anyway. The guy that did it used a lot of numbing stuff, but it didn't do anything and I felt the needle the whole time - that was a weird experience. Then there was all the blood, it's amazing how many tiny blood vessels there are in the tongue.