This little contraption is an adaptation of a keyhole spy tool. Real spies used it in the past to look through keyholes.
Well, anyone can look 'through a keyhole'of course (duh!), but this one actually gave an opportunity to get a fisheye view of the room. This was not enough to recognize who or what was in the room, but this nifty little tool could be poked into the keyhole, and be used to see if there was any movement in the room.
Better be safe than sorry!
Nowadays, we just stick a camera with glass fibre cable through the keyhole, of course. But it still is fun to make this little tool, that reminds me of the good ol' days! Aah!
Put the marble in the middle, and roll the paper tightly around it. Stick it with the sticky tape. THen blow, or poke the marble to one end until it's just sticking out. The half of the marble will still be inside, and half of it will peek outside...
Here's a picture of the end result:
The only trick is, that the entire picture is upside down! This is because the marble will reverse any light that falls through it.
It's just a simple tool, but, believe me, very effective!