'Will' chuckled. "Observant, aren't you?" He walked across the room to a silver briefcase. He opened it, extracting a test tube full of a green liquid. "This is the T-virus," Birkin said, holding it up and smiling. "When a human is infected with it, they become what are essentially zombies. Eventually, given the right circumstances, they'll turn into one of those." He pointed at the Licker.

Birkin took a sip from a half-full coffee mug that was lying next to the case with his free hand, before shutting it tightly and walking back to the examination table.

He held out the vial to Stein. "You can keep it and give it to your bad students if you want; we have plenty. Besides, it's not terribly hard to make more." Especially considering they were in the right area in Africa to find the 'ingredients'.