Okay, you're a wimp.

There are a few indicators that you can watch out for. Most commonly is the tell-tale "Hiss" that they make. They usually do this when you wake them up and try to pick them up. However, I've found that if they hiss, they usually don't strike. The ones that have struck are sitting in the classic 'S' position with their head raised up. When that's the case, I usually just move my hand behind them and pick them up, then they usually calm right down.

BTW, I can understand your aprehension to getting bit, but a bite from a Ball really isn't a big deal at all. It's not exactly a ticklish experience, but nothing to be very concerned about.