to go behind someone's back

verb: to follow closely behind, or to check (someone) frequently, implies that the action causes some annoyance or interference (from the fact that a pet dog will often follow closely at its master's heels).

Similar in some senses to 'hound' as a verb.

Amongst Australian criminals Dog is slang for Snitch.

An animal you see every fucking day if you don’t live in the middle of nowhere

Swearing on the lives of all of your closest friends.

The dog is a domesticated canine which has been selectively bred over millennia for various behaviours, sensory capabilities, and physical attributes.