Bad Bean Sprouts

Someone came to my blog today because they searched for "bean sprouts how do you tell when they are bad?". My instant thought was, when they are moist, sour, or gray. Is there another way?

I know there has been some hubub recently in the Candadian press (and yes, this was a Canadian visitor) about bacteria and bean sprouts.

So--how DO you tell when bean sprouts are bad?