aswani mudra

literally, the "seal, or gesture, of a horse" being a rapidly repeated contraction and release of mula bandha, q.v. Used to strengthen the anus sphincter muscle in preparation for holding the bandha. (If you have ever spent much time around horses, you'll immediately recognize the reference for this technique: it is the method horses use to produce those near-perfect spheroidal feces of theirs. Rabbits probably use the same technique, but since their anus is not at human eye level, it's not nearly so obvious.)