their mouths
Examples
Look at these humans! How could such glacial slowness even be called life? An age could pass, virtual empires rise and fall in the time they took to open their mouths to utter some new inanity!
O God, that men should put an enemy in their mouths to steal away their brains!" - Cassio (Act II, Scene iii)
Why, all the Saints and Sages who discuss'd Of the Two Worlds so wisely - they are thrust Like foolish Prophets forth; their Words to Scorn Are scatter'd, and their Mouths are stopt with Dust.
Bees that hae honey in their mouths hae stings in their tails.
Similar to a bee: in their mouths they carry sweet honey, and in their tails poison.
Money has the capability of making people laugh; but when they laugh, the foolish ones sometimes forget to close their mouths.