Eyecatch Cel

In many anime series', there is a commercial break about halfway through the episode (depending on its length).  To demarcate these breaks, sometimes a quick animation will play. These are often repeated throughout a season.  In some cases—Sailor Moon is an example—there is an animation both before and after a commercial break.  In other shows (Fullmetal Alchemist is one), there is simply an image that flashes, and they are different for every episode.