I've never tried freezing them. Gonzo is always watched when he has his, and he has never bitten off a large chunk... he usually gets medium sized greenies anyway, so I don't think he could easily choke on them even if he swallowed it whole!

I actually started getting him Nutri-dent bones by Nylabone. They have almost the exact same ingredients as Greenies, but instead of getting two for $5 with greenies, you can get 5 for $5 with these. here's a link! He *loves* them just as much as greenies, and they make his teeth nice and shiney! of course he gets raw bones on top of those..