this is really great.
I save plastic bottle caps from the 16.9 ounce spring water bottles to string onto toys sometime, and have alot of them built up. I also be sure and give them a good washing & steralize them for a few seconds. They are the kind of clear ones, not colored, and they do not have that adhesived plastic piece inside like some bottle caps do. I would assume they are safe. He loves to play with them.