What use is even attempting to take an item if you don’t first consider what to take? With deft hands it is simple to know what your unsuspecting victim is carrying in there ‘secure’ backpack.
Snooping allows a player the ability to peek into another belongings. Using this skill before attempting to steal will allow one to specifically target the item they are looking to acquire.
To peek into a players backpack the thief must be right next to the target and then attempt to open their backpack from their victims paperdoll. There is a chance that while doing this your target and others in the area will be informed of your devious behavior.
Snooping is not considered an aggressive act by the local authority but is frowned upon by other players. As such you will not be subject to the quick retribution of the guards, but don’t expect players to stay near you while you attempt to inspect their belongings.
After learning everything you can about snooping from your local thieves guild representative gaining the skill is as simple as attempting to open a bag that is not yours. The same pack can yield skill gains countless times so finding someone to let you stand next to them can raise your skill quickly.