I once worked in an office that would always end department-wide emails with a gif of a cute animal. It happened so often that it became an unofficial rule in our office. People would be upset and complain if a gif was left off an email.
One day I noticed that mammals were getting all the love so I attached a gif of a snail to try to mix things up. It was this gif, to be specific.
People were furious with me and shortly thereafter people stopped sending animal gifs to each other and morale dropped. I guess the lesson here is never try mess around with the rules, and never, ever show a mollusk love.