Human Snag his finger

He looked up at the sign, and he reached, digging fingers in where the sign and the wall were.  He stepped on someone, tried to climb toward the window, eye on the latch, darting over to look at the smoke behind him, then up to where the smoke was thick near the ceiling.  The plexiglass front of the sign was a hinge, so it could be opened, and he dug his finger into that gap for the leverage it could afford.

The climb would have been hard on its own, but he was jostled.  His hand slipped, and both his fingernail and the tip of his finger tore off as his hand came away from the hinge.  A thin streak of blood was drawn on the plexiglass.