A recent post at Reisner Veterinary Behavior Services talks about people who are not aware of this and think belly up is asking for a belly rub, ending up being shocked when they get bitten.
Like kissing, the belly-up position is one of the most misunderstood interactions in the human-dog social lexicon.... It’s not uncommon for dogs to lie still while their belly is being rubbed, then quickly snap or bite at the hand as it’s withdrawn. (While the hand is doing its rubbing, they are likely in “freeze” mode, quickly “thawing” to a defensive bite when it’s done.)...Is rolling on the back ever an invitation to pet and rub, then? ...Unless you know your dog very well, it is safest to assume they’re uncomfortable. A good test is to sit nearby or walk away, clapping your hands and talking in a silly, happy voice. Most dogs will flip upright and join you happily, unstressed.
Dogs don't bite out of the blue. We just need to have the right phrasebook.
Photos by Yakob Miyajima