While we're on the subject of big mouths from my previous post, here's a shot of one whale mouthing another during a period of intense social interaction:
This playful mouthing seems to be a normal and frequent behaviour, as we've seen it many times in the social groups.
It doesn't seem to involve aggression, and there doesn't appear to be any serious force involved...sort of reminiscent of the way puppies in a litter play-bite one another...but more gentle.
Note: Photo taken under permit.