At Rank 1, you can notice hidden objects, such as traps, on the ground and in chests. The success rate for doing so increases with Rank. For objects on the ground, you will automatically notice, but for chests, you must Search For Traps. To do so, right click the chest and select the appropriate option, or Ctrl+Left Click the chest. Some chests may not need to be searched.
At Rank 3, your experience has given you expectation; you know how to read enemy movements and predict them. You gain +5% Skill growth permanently, thanks to your training.