Ha. I had the opposite - 'push, push!' while I screamed I AM!!!!!! Didnt' think I could push any harder if I tried.
Epacris, I think you go (to a certain extent) with what your body tells you. If you want to hang there & scream, do it screaming has always worked well for me.

ETA - I should add, I was being a bit tongue in cheek. I can see the benefits in directing some of that screaming energy into pushing, like Keiki said, and I realise there are times when it's best not to push - you can't always just do what you feel. But I just hate the whole feeling of being directed, instead of encouraged or coached, at that time. Working with what you feel would be so much nicer, if you can, I think.