The second key

An original fiction passage set in the nineteenth century.

Robert returned the key to its hook. It hung beside a smaller one he had never seen before. He reached towards it, then heard his aunt’s step in the adjoining room. Curiosity and caution pulled him in opposite directions. He straightened the familiar key instead and asked whether she needed help carrying the tea tray. When she left the passage, he remained where he could see the hook.

Identify the sentence which shows that Robert has conflicting feelings.