In theory, you can put any image in an animated eight-frame loop. (In the 1990s, people used grainy, animated “under construction” gifs, ornamented with hard hats and traffic cones, to apologize for portions of their homepages that were incomplete.) In practice, the gifs of the 2010s are reaction gifs: silent, looping animations of people, animals, or cartoon characters doing a specific, expressive gesture which you invoke as a representation of your own body under the circumstances, saying that right now you’re laughing, or applauding, or looking around in bewilderment, just like the person in the gif is.