What does "serum" refer to here?
A "serum" is a protein-rich liquid that helps humans fight off infections or poisons. It is commonly applied to the outer layer of the skin or can be injected underneath the skin. In this scene, Gru and Lucy are in search of a mutant serum that if injected into a person, will change any living being into a purple mutant. The serum in this clip does not fight of a poison but puts a mutating poison into that person.