Miqula did that, a lot, when I first got her. I'm not sure it was really fear, and not irritation - if I set it down, she'd slither all over the top of it looking for a live one, and completely ignore the f/t one no matter how warm I got it. Just if I tried making it 'dance' for her, she'd strike and not grab. I don't know that that's any help... just my own experience.