her tendency to act without forethought
The big downfalls for both Romeo and Juliet are their impulsive behaviors. In this Juliet does not stop to think about the fact that she will be actually killing herself this time. Before it was only fake, now it will be real. Her first reaction to seeing that Romeo is dead is to join him, so she tries for a drop of poison that may still linger.
Armory is the correct answer I believe
Thanks for the free points
