If by "behave very unusually" we mean "channel outward like a very small flamethrower".

The man, who's closer, recoils with a shriek and starts flailing to beat away the flames rising from his coat front and muffler. The stream of fire from the lighter follows him as though magnetized.

The other one makes a strangled noise of pain, but instead of flinching back she moves forward, arms reaching out to grab him as though intending to smother the flames between them -- or as though intending to bite him even as she burns.