It's not your dog and there are so many bad outcomes possible from messing around behind your sister's back. Some of them will get the dog hurt.
wright-oneursidae canidae pantherinae 2 points on 2017-08-09 03:53:59
well, this probably isn't what you want to hear, but .. go alone somewhere and masturbate. it's not your dog, first of all, and second of all, i don't know how big this dog is, but you might hurt it by trying to have sex with it, and third, you don't know if this dog would want to be fucked up the ass; some are ok with it, some aren't.
i understand the desire, but you have to keep it in check for the above reasons and more, such as... how would your sister feel if she found out? etc., etc....
zootrashcandoggy doodle dandy 1 point on 2017-08-09 03:59:16
Nothing. It sounds like you don't have permission, so. Not your dog, not your call to make. You need to have the consent of both the dog and the owner. If something goes wrong (dog gets injured, you get bit, you get caught, etc) you've put the dog, yourself, and your sister in a situation that's awkward at best and dangerous at worst.
the_egoldstein 1 point on 2017-08-09 04:02:03
Sorry to pile on, but another bit of advice to curb yourself.
I've nothing new to add, but merely upvoting the other very good replies I don't think is obvious enough. Don't do it, respect your sister and her family (dog included). So many possibilities for that to go horribly wrong.
/r/zoophilia archive
Go to the shower and whack off.
It's not your dog and there are so many bad outcomes possible from messing around behind your sister's back. Some of them will get the dog hurt.
well, this probably isn't what you want to hear, but .. go alone somewhere and masturbate. it's not your dog, first of all, and second of all, i don't know how big this dog is, but you might hurt it by trying to have sex with it, and third, you don't know if this dog would want to be fucked up the ass; some are ok with it, some aren't.
i understand the desire, but you have to keep it in check for the above reasons and more, such as... how would your sister feel if she found out? etc., etc....
Nothing. It sounds like you don't have permission, so. Not your dog, not your call to make. You need to have the consent of both the dog and the owner. If something goes wrong (dog gets injured, you get bit, you get caught, etc) you've put the dog, yourself, and your sister in a situation that's awkward at best and dangerous at worst.
Sorry to pile on, but another bit of advice to curb yourself.
I've nothing new to add, but merely upvoting the other very good replies I don't think is obvious enough. Don't do it, respect your sister and her family (dog included). So many possibilities for that to go horribly wrong.