my friend literaly got "Raped" because she did not know dogs can fuck humans so she was naked. he humped her and she responded with laughing untill he got in then she was shocked and when it swelled she tried to depart from him but it was too big. off course she loved it, and that what made her get into it and she continued. but it is "sort of rape" because she only was willing after she proccessed how much she loved it after the act.One can't be raped by a dog. Sure some dogs can get very sexually aggressive. But a human can easily stop any dog from taking it that far. Besides, a dog doesn't know what "Rape" is. Also it isn't rape if the person wants it. So again if the person doesn't want the dog have sex with them, the human can easily put a stop to things before it reaches that point.
I also agree that's it's a nice fantasy for some. But that's about it.