A4 paper/ rectanglar (can be smaller)
1 piece
Tape/glue
This is sharp but it gets blunt easily.
Get a peice paper
Fold the the bottom line to the side line as shown
Fold rectangle down
Flip it over
Fold the triangle up
Turn the paper 180° clockwise. Fold it in half as shown
Fold it again
Fold it one last time
Now tuck it in
It should now look like this
Final results.
You can put your finger in the hole.