My rat just ate a Hershey kiss?

I was letting him run around on my desk and I forgot I had a Hershey kiss here, and he ate a bit of it (I'd say about 1/4 of it before I grabbed it from him, so really not that much) it was plain milk chocolate. I'm not terribly worried about the chocolate... but is there a way I can make sure he didn't eat any of the foil? It looks like he just shredded up most of it, but idk if he swallowed any...