The dogs are Yorkshire TERRIERS - and terriers are hunters. They aren't out there in the coal mines huntin' up rats, so they exercise their genetic imperatives "killing" squeeky toys. It's what they do, built into their DNA, and they usually know the difference between play and people. Once mine got past the real puppy stage (4-6 months), there was no "teething" on fingers.
I think it's a real hoot watching them shake the stuffing out of toys (sometimes literally

). They stalk, pounce and "kill" their intended prey. Toys are much better than the REAL thing