Because they can't see if they close both.
Ventriloquists have to be able to speak with their mouths closed. Politicians speak out of both sides of their mouths simultaneously.
To keep an eye on the exit
She bats her eyes.
If they squirted it through their tails it'd be very difficult to aim.
The game warden found out he poached his eggs!
The hunter has to wait until it's in season!
