The Over the Mouth gag, commonly abbreviated as OTM, is a common gag used amongst light bondage subjects. An OTM gag works by taking a piece of cloth and wrapping it over the subject's mouth, similar to a tape gag and cleave gag. Unlike tape gags, the OTM gag is not sticky, and must be tightly bound in place behind the subject's head to remain in place. Although the binding motion is similar to a cleave gag, an OTM gag is non-intrusive, and does not enter the subject's mouth.
This is a simple type of gag that was popular in mainstream film, especially in crime serials of the 1930s and 1940s. For this reason it is also called the detective gag.
OTM gags are probably the most comfortable gags, as they do not intrude or stick. They are also probably the least effective gags, as they do not block tongue or mouth movements, and must be very tight to block lip movements. They are popular in television shows, as the subject wearing the gag may prefer to have a light gag, although still trigger a sense of helplessness.