Our Beagle puppy does that too! We also thought he was pretending to be a cat. He seems to rub himself on everything until he gets so low he is laying on the ground and then he will continue to crawl along on his belly for a while...
It doesnt seem to be him trying to rid himself of an itch though...
We will be speaking to the vet this week about so he can have his 12 week shots, will let you know if I find out anything...