Hanna and Spencer are stealthily infiltrating some sort of laboratory, but why? Considering we know they are going guns blazing after Lesli, my best bet would be it's connected to proving she is their tormentor.
What are the significance of these animals to the episode? Did Mona throw one at Aria in the hopes that it would bite her and make her ill? Quite possibly. Nothing's shocking in Rosewood.
Emily is less than impressed, but why? Whomever this sick, twisted individual is, must clearly be someone close to her group of friends, but will this be a Liar reveal, or a viewer reveal? I'm not so sure!
