What are the words to a Counter Curse?

In Harry Potter and the Philosophers Stone, Severus uses a counter curse, (as we find out by Quirrell) to attempt to aid Harry from falling off his broom. Quirrell, in fact was using a curse.

I do not believe Quirrell put a specific spell on the broom, but was just muttering a curse. If it was a curse, what kind of curse, and did it need a specific counter curse, or was one counter curse universal?

Anyway, my main question is:

What does a curse sound like? What are the words?

AND

What does a counter curse sound like? What are the words?