Could it have been an abrasion from the inside out, like passing a little sliver of a dry bone that she may have found and eaten? Try as we might, when going off leash in the wild, they can find little pieces of stuff and eat and swallow without us seeing a thing... Asha finds really dry old bones like deer leg bones and when she bites down on it, it shatters like glass. I know she gets some of these every so often and if I yell at her to put it down, she does, but she swallows whatever little pieces are in her mouth.