This is a method comic artists use a lot in comics to demonstrate agility and speed. In this method a character is drawn several times in one panel in different poses. They do this a lot in comics like the Flash, Quicksilver, or Spider-Man. It is also used to show transformations, like Banner turning into the Hulk or Hulk turning back to Banner, or Ben Grimm becoming the Thing, or Giant Man or the Atom growing. Animated Panels can also be used to show a character's combat skills, like in Iron Fist or Captain America.
Giant Man Growing to giant size using an Animated Panel.
Hulk transforming back into Bruce Banner using an Animated Panel.
Flash demonstrating his speed with an Animated Panel.
Spider-Man's agility being shown in an Animated Panel.
Captain America demonstrating his Super Soldier enhancements in one Animated Panel.
The Atom shrinking in an Animated Panel.