IIRC Snowden said he used similar tricks to see if his hotel room had been searched. One was a cup of water behind the door, that would be knocked onto a tissue

IIRC Snowden said he used similar tricks to see if his hotel room had been searched. One was a cup of water behind the door, that would be knocked onto a tissue that he'd sketched a hard-to-reproduce drawing onto. I think he mentioned another method that I've forgotten, but the pencil lead trick sounds familiar, so that could have been it He was also known to be into anime, so he could well have seen that scene too