As Zim explains to GIR, a drop of the humungoserum can transform anything into a giant monster, which he demonstrates on a bug, before destroying it. He then goes off to his "scheming nook" to figure out how to use the humungoserum against the humans, having apparently not done so beforehand. It is at this point that Dib, having learned of the humungoserum by spying on Zim, steals it as proof of Zim's plans. He succeeds, but upon escaping from Zim's Base, is kidnapped by a pair of aliens, and swallows the vial containing the humungoserum to hide it.