Eyes rolling sideways when chewing a rawhide treat

Hi there, has anyone witnessed or noticed their chow chows eyes rolling sideways (so you can see the whites of their eyes) it only seems to be when she’s chewing a rawhide stick and is chewing with her back teeth. She’s completely fine in herself and is normal, well as normal as a chow chow can be, but I’m worried something could be wrong. Only asking before taking her to the vet to see if anyone else has had the same thing happen and can offer any advice. Cheers