Flail
This term is a holder subtype.
A flail is a headmate, no the matter alter age, who represents the body's repressed or latent urges to do excited and/or "childish" things. They tend to be less restrained in action, and much more childlike and silly. They may be seen as or appear as littles due to exhibiting some little traits and behaviours, however they typically aren't littles.
Some behaviours they may show might include visible stimming.