[Help] Does anyone know why my dog does this to my other dog? Pics included.

My female Shar Pei presents her genitals and stands over my male Bulldog and he then sniffs and kicks her there. This happens multiple times a day, mostly when we're laying on the bed or they're resting on the floor. Both are fixed and have been for a while.Pictures: http://ift.tt/2sFoj96 via /r/dogs http://ift.tt/2rHoweN