 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 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 . 
