aluminum foil/foil bag

I know that it is bad for cats to eat aluminum foil. What happens if they do? My cats were home alone yesterday and one of them had the bright idea to chew through a bag of treats. I hope they just ripped it open, but I fear they may have ingested some of the plastic/foil bag.

What do I need to be watching for? They both seem fine.

Thanks!

I've heard its not a bad thing, and that they like the texture. My kittens havent had a problem with it, but let some more of the experienced posters back me up before you get going with it...