My dogs do it all the time, esp Lily, my younger but bigger dog. She waits till Winnie nibbles on her toy and then Lily goes and nibbles on Winnie. Lily doesn't play with toys or play fetch; she just uses Winnie as her dog toy! Winnie seems to like it. They also lick each others ears a lot, well mostly Winnie licks Lily. They take care of each other.