What is with the trope of using a glass to listen through a wall or door? Surely it doesn't work, right? Do all of these people have glasses with no bottom?

It's like when you see in TV/movies when someone gets tied up and "gagged" by just putting a sock in their mouth with no tape or anything. As if the person couldn't literally just spit the piece of cloth out.

Takes me out of it completely, every time.