Object hair will not comb

I am using Blender 2.65 and trying to follow a carpet tutorial. In the tutorial, the carpet is combed in particle mode and it affects the carpet strands, which are a group of objects. However, when I tried this, the carpet was not affected at all by my combing. Here is the result when I combed the hair completely to one side:

Does anybody know why this is happening?

Thanks so much