The dog filter finds its inspiration from the female dogs, also known as bitches. It also represents the dog society. In which the female dog of a pack has to submit to the male alpha dog.
When a girl has the dog filter on SnapChat she probably sucks off he entire football and soccer team or if so they are hugely acosiated with suckin dick
Friend: Bro I just got given heads by this girl she sucked offthe hole soccer team
Me: she probably uses the dog filter from snapchat