Do you bite fingernails when you are bored or stressed?

I just finished reading Nick Leeson's Rogue Trader. He mentioned that he had a habit of biting his fingernails when he was stressed. I remember when I was studying for my diploma, there was a very outstanding lecturer. His teaching method was very lively, and he was very humorous. He loved to initiate discussions, and engaged all of us in the discussions. The most irritating part was that he bit his fingernails when he was not talking. It was so gross to look at him, and saw him biting the fingernails. Do you bite fingernails when you are bored or stressed? Do you have any outward show of stress, such as fidgeting?