Invisible thread

Exploration Stage: Negotiation Room
From: Pawnbroker
Description: Please go through the memory vault and find out together what the thief took. You will be rewarded, of course. The culprit may be a very smart person, if he or she was able to evade the traps set by the vault's security system. But he or she missed something. Look at the doorstop.
Completed: You have a keen eye to immediately notice that these two doorstops are tied together by a very thin thread. The fact that this thread is broken is a sure sign that someone has broken into this vault. Sometimes the very simplest methods are the most effective.