Placing a gag on anybody is very risky, as it involves a substantial risk of asphyxia if the subject’s nose is blocked by the gag. Using a gag on somebody who is ill, or affected by some condition such as the common cold, catarrh, or the flu, is also quite dangerous, as most gags inhibit breathing through the mouth. Vomiting and choking is also a risk, which further blocks the airway. For this reason, a gagged subject should never be left alone.
In practice, no gag is effective enough to completely silence someone without inhibiting breathing. Most gags that do stop the subject from making intelligible speech still allow loud inarticulate vocal noises to call for help. Thus, a pattern of noises, such as three grunts in rapid succession, is sometimes used as a safeword by BDSM players. It is also common to use an additional non-verbal safety mechanism, such as a solid object held in the hand, which can be released by the gagged person as a sign that they are in distress.