Some people believe their dogs understand everything they say, while others claim dogs only understand facial expressions and emotional responses, but most animal behaviorists agree the truth is a combination of the two.
Dogs can understand words their humans say to them repeatedly, and they begin to associate things like mealtime, praise and admonishment with those words, the most popular being the praise "good dog".
Redditor JavaReallySucks posted a pic of his adorable dog before and after being called a good boy, to illustrate the way his dog's face lights up after being praised by his master.
The photographic exercise seemed like fun so others took to shooting before and after praise pics of their pets, which worked really well with the dogs while the cats continued to not give a crap one way or the other.
See People Are Posting Pics Of Their Animals Before & After Being Called A Good Boy here