Adam writes...

THE HYENA CONTEST

Hyena smiles because she's amused by Elisa's values. Elisa is clearly playing by the "good guy" rules, which say that you don't shoot someone when you could arrest them, you don't drop Xanatos off the building, etc. Hyena believes that when it's in your best interests for someone to be dead, you kill them. It's funny to Hyena that Elisa could be so deluded by ideas of "right" and "wrong" that she would let someone as dangerous as Hyena live to fight another day when it would be so easy just to kill her and solve the problem permanently.