[doggiedad]

i've always used femur bones (beef) cooked and raw.
when they were cooked they were baked for 20 minutes or so.
i've never had a femur bone splinter.

Yup, it's because of the bone. Be careful how much edible bone you give; too much will constipate your dog. You should also avoid cooked bone because it splinters and can potentially be very dangerous for your dog. Raw and frozen raw bones are safe.