Puppy play and "Pre-mounting"

[Cammie Hensley]

We have been taking Riggins (14 weeks) to training classes once a week now for 4 weeks. He was timid and overwhelmed with all the new smells and puppies the first week and has slowly become much more comfortable, outgoing, and confident. We thought this was great until- until last night.

Last night during the play time, one of the trainers noted Riggins exhibiting what she called "pre-mounting behavior". Basically, Riggins stands over a dog that has rolled onto its back and slightly arches his back as if mid-hump. She said we should "watch" for this behavior and interrupt it when it occurs. She asked if he gets to spend time with other dogs (which he does, generally a few times a week), as this is what she describes as "socially-awkward behavior" and, I'm assuming, something that dogs with social deprivation develop(?) 

Does anyone know anything about this? Why he does this, what it means, what we can do to help stop the behavior, etc. I did a search on the site and on the web and didn't find anything about pre-mounting, only actual mounting. He has only actually mounted anything/one once a few weeks ago. 

[Cammie Hensley]

Oh, I'll add that most of the other dogs he has played with are much bigger than him, and has had a negative experience with one small (poorly socialized) dog. Could it have to do with the fact that he is playing with dogs of similar/smaller size than him?