"Thief II" is designed to be played methodically, and the player plans ahead by scouting, reading the game's map and observing patrol patterns. The player character has a zooming mechanical eye, which connects to throwable "Scouting Orb" cameras. One Scouting Orb may be deployed at a time; when it lands, the player views the game world from its perspective until normal play is resumed. The player can listens for noises, such as footsteps and humming, to determine the locations of enemies. On the highest of the game's three difficulty levels, killing humans results in a game over, and in certain missions the player must not knock out any guards.