Curling:
It can be very easy. About three years ago I was squatting 315 three sets of 10 reps. On my warm up set with 185, I went down too fast and my right knee popped. Extremely light weight, I just didn't think I could get hurt. Now, I go real slow with squats. I don't go so heavy (I'm back up to 315 for 8-10 reps, but my form is so much better and I get a better burn from it) anymore.
Also, I do pause presses a moderate weight. (You know, take the weight down pause for 2 seconds and then bring it; it burns baby.) Do 10-12 reps, works very well. I ussually to two sets of these before getting into my regular sets.