It's all relative

Overheard this conversation during lunch today:

B- I have a dog. She's a good dog.
T- Oh, that's cool dude.
B- My dog is a girl, her name is Rawly.
T- Oh.
B- My dog is a girl, so she is my sister because she's a girl.
T- * Blankly stares off into space clearly tired of this conversation*
E- Your dog is what?
B- My dog's a girl so she's my sister!
T- *snapping back to reality* What? Wait a second dude, how can a dog be your sister?
B- Cuz she's a girl.
T- Ah man. That's weird.