My girl has struck at her heat emitter before too. I think it happens when you move them into their tank. I've started to just hold her up to the door and let her crawl through on her own and I haven't had that happen again since. I think the sudden heat signature spooks them. Even more so when they're already nervous or feisty since it's right over their head. Just my opinion, I could be wrong, but it doesn't hurt to try.