My mom's 12 year old doxy does this!
He kinda sucks on the toy. We have always attributed it to the fact that he was weaned at 5 weeks old - but who knows!
My Rowdy occasionaly puts a toy in his mouth, then kinda zones out, but he just lays down with the toy in his mouth, he doesn't knead or anything.
I don't know what it is!
