Daisy does this all the time -- the larger and floppier the toy, the more she likes it because she gets more 'swing' out of them. She growls like a little vicious thing! It totally cracks us up. She did this from day 1. She doesn't like any type of toys but soft and furry, and preferably animal-shaped. I think this is because rubber toys and balls don't shake effectively. And she requires squeakers in her toys, too. It's no fun killing something if it doesn't squeal!
And she loves to play tug of war with us using those toys. She growls like a demon. But she would never bite us. If someone else saw her do that, though, they would think she was Cujo!
Sadly, all this practicing of the death shake came to fruition this past Spring, when she killed a baby bunny!
I didn't see it happen, but she brought the poor little thing in the house, hanging limply from her mouth. I freaked out, needless to say. We buried the poor little guy in our backyard under some trees. RIP