You quickly close the door shut and tell your class to stay calm, explaining the situation that is happening outside.
lol man, I don't think anyone will react like that. The typical reaction will probably be to scream and run like crazy, throwing chairs at the zombies and trying to escape :P
and run like no return...pak!😅
Hahaha... I don't know man, there was a fire once and some stopped to take a selfie... Zombies are rather instagram worthy