they walk down the hallway and hear a weapon click. A weapon is pointed at them. They stop.
A door opens. They both look. 
The person walks toward them. 
"Stop right there!

They freeze. They drop their vials to put both hands on their weapons. The vials drop to the floor and scatter. 
"Get out of here!"
S/He picks up the one undamaged vial.
 S/He takes off down the other way in the hallway.  
"Stop right there!"
The bullets go right through them. Green oozes out of the holes. S/He runs down the hallway. S/He turns around. Their eyes start to water. S/He drops the weapon, gasps and grabs their eyes.