[His reaction earns him a nonplussed look, followed by an assessing squint. She'd expected some alarm, sure, but not "attempted fleeing".]

Sorry, didn't mean to scare you. It's just really cold and I figured cozying up to someone for body heat was the least alarming thing I could do here.

[She's not sure if anyone in this car has seen her shift yet, and she doesn't want to have to make a big announcement about it to keep everyone from freaking out. She's cold and she's exhausted, and she'd figured it'd be far easier to bully a big burly white guy into letting her into his space.]