His assistant has steady hands.
It's one of the first things about her that truly registers to him, that stays in his mind and distinguishes her as more than just another presence in the lab there to hand him things over a cadaver. Other things start to come gradually and attach themselves to form the cohesive not-quite-whole of his memory of her. Her patience. Her curiosity. The way her wondrously curly hair smells slightly of ginger. The little sigh she would let out before cleaning up the mess he had made. How she would give him her full attention – her warm brown eyes bright - when he was telling a story.
But his first and constant impression of her is steadiness.