I couldn't find anything about this so I'll post my findings here to see if this is known (and perhaps part of an Easter egg??).
There are several location where you hear a girl laughing when throwing a monkey bomb. Same audio as when the box moves to another place.
For example the room where the Zombie is hanging from the sealing, the wells near teleported B, several zombie spawn location and when thrown in the rooms that are set on fire.
Is this known or did anyone else notice this?
Btw, when this is done, the Monkeys are "useless" as they won't attract any zombies.