Sam didn't really know any better. He just knew her hand felt good and that the urge to mate was really strong. He wanted more of that pleasure and just keep humping and yipping away.
Barking at the suddenly lack of pleasure, Sam's attentions were soon turned as he noticed Jenn had removed her underwear. He knew this, because his keen sense of smell detected a fertile pussy that was gushing wet. Yipping with excitement, he dove for her pussy. Trying to lap at it with his long tongue.