bite your tongue

You force a creature to bite their own tongue as they attempt to use it. The target makes a Wisdom saving throw. A creature Immune to the Charmed condition automatically succeeds on the saving throw.

On a failed save, they must immediately make a Constitution saving throw, taking 4d4 slashing damage on a failed save, or half as much on a success.

On a successful Constitution save, they are unable to speak until the start of their next turn. If they were casting a spell, the spell dissipates with no effect, and the Action, Bonus Action, or Reaction used to cast it is wasted. If that spell was cast using a spell slot, the slot isn't expended.

On a failed Constitution save, the creature is Silenced for 1 minute, or until it restores any hit points. A Silenced creature is unable to speak or cast spells that require a verbal component. At the start of each of its turns, it can repeat the Constitution saving throw, ending the effect on a success.

Guess that's what happens when you chew over your words too much.