I remember the first time - probably around the same 4 months mark - that I witnessed Kensington hump his stuffed turtle. I was shocked, mostly because he only weigh around 1 1/2 pounds at that point so he seemed like such an innocent little baby. When I asked my vet, she assured me that it wasn't sexual at that stage. It is an alpha dog assertion thing or something - very instinctual. In fact, you'll see the female dogs do the same thing. They are working out their role in the pack. I'm, of course, no expert - but that is what I was told. Hope that helps!
