In the movie split, a white cloth is shown which is kept by Kevin's therapist in between the door when she came to meet Kevin. The cloth is shown again near the climax scenes too. What does that mean? I couldn't find any connection and I am afraid I missed something relevant in this regard.
Dr Fletcher asks to use the bathroom, and discreetly stuffs a napkin in the lock of the door so she can't be locked in. That's the importance of the napkin.