A butterfly gag is a type of gag sometimes used in sexual bondage practices found primarily in BDSM. It gets its name from its design which, when inflated, resembles the wings of a butterfly.
Butterfly gags are worn by submissive partners. The central part fits behind their teeth, while the wings sit between their teeth and lips.
A rubber bulb typically inflates a butterfly gag. The dominant partner inserts the butterfly gag. Then they inflate it so that the central part of the butterfly gag perfectly fills the submissive partner’s mouth.