Here is some information from a website about “gimp masks” and the dangers in masks with covered mouths. It also explains WHY the mask is used in the context of bondage and domination sexual roles: https://www.lovense.com/gimp-mask
Essentially, a GIMP is one that submits to another for interpersonal exploitation. The GIMP wears a mask to designate his/her/their lowly status:
The featureless face covering is meant to depersonalize and objectify the gimp, so that they might be exploited and used without empathy getting in the way.
Additionally, “breath play” is a part of obstructing the breathing of the GIMP.
CAUTION: MASKS WITH NO HOLES OVER THE MOUTH OR NOSTRILS CAN RESULT IN ASPHYXIATION: