Instruct the players to start whispering (you are a player).
Decide among yourselves a fictitious reason you are all whispering (you're 6 years old and built a couch fort-parents are in the other room and if they remember you, they'll remember your bedtime; your friends are trying to sleep in the back seat of the car while you chat up front; the killer is close but you have to coordinate; etc.)
Play out the situation as your character, and/or with narration and description.
The game ends when someone speaks without whispering.
Variant: Big Voices
Instead of whispering, yell. The game ends when someone talks without yelling.