Of course a dog cannot be homophobic. Dogs simply do find something as loathsome and disgusting as anal penetration an indicator of submissive behaviour - and so IS it -, and dogs are domesticated wolves. Wolves have a strong sense of hierarchy. Besides, I am also almost completely sure that dogs find anal penetration disgusting for obvious hygiene instinct and also for another obvious instinct: avoiding pain and avoiding anal tearing and fissures. About frot, It IS not just dogs; almost all mammal species do It for the same reason we men - and also women - do It: It IS undoubtedly pleasant and joyful. That's the reason dogs, both male and female, rub their genitals against our legs. Since mammals - except humans - are four-legged and so cannot use their upper extremities for the same purposes we do, they cannot masturbate as we do; they have to rub their genitals against something, be it our legs or any other thing, such as another animal genitals, which is more pleasant than rubbing against any other thing. (By the way, I would find unbearably hard being unable to use my hands to love myself and having to rub against something to work off sexual tension; I'd rather be given a hand by a bud, no doubt).