They are chasing this guy into an aquarium, Dick makes some really difficult (and flashy) acrobatic jump across a tank with killer whales, Tim uses a line to swing across, but one of the whales jumps at him and Tim looses his grip, falls in and has to swim across (while reassuring himself that at least there's no record of these whales killing people) and finally climbs out of the water. So in the icon we see Tim climbing out of the tank, and Dick being kind of smug.