Houdini was very interested in psychics and "mediums", and spent a lot of time exposing them and training others to do so.
He devised a simple test: he had a pencil suspended by rubber bands over a pad of paper, and in a closed, wrapped, sealed box. The challenge was to cause the pencil to write something on the paper. It never has.
The box was in a museum in Niagara Falls, Ontario ("The Houdini Magical Hall of Fame"); here's a page of an article archived at https://dn721805.ca.archive.org/0/items/harry-houdini-magician-or-psychic_202403/Harry%20Houdini%20-%20Magician%20or%20Psychic_text.pdf
Unfortunately, it must have been lost in the fire which destroyed almost everything in the building on 1 May 1995.
