Chloe had way too much experience when it came to Clark and his understandable fear of green rocks and green liquid that could kill. She saw how his reflex action was to move away from the source of death, since mortality came from home.
Davis did nothing to escape the end. He looked up, catching the green death that showered mercilessly on him. He could have ran to the latch and easily unlocked making his escape. There was a chance for him to rip flesh with spikes and shatter six inch thick glass.
Chloe had ran up to him, putting her palm on the glass, a silent urge to not give up. She didn't want to kill him. She just wanted time on their side. She just wanted him.
With love on his side, and death in his face, Chloe shuddered with grief at the heartwrenching realisation of something familiar. He did not flinch.