Right. This game has the mechanic of "The more you have sex, the different the pose" (in most cases)
The basic is 10 times before you can see a noticeable change (not necessarily 10 times in the milking parlor, just that the fapets already had sex 10 times in general).
You can try using a Kelpie or a Horse with a bunny, the fapets will some special movements sometimes. The horse French kiss the bunny for example