Catholic church I attended had an alter with a small space between the floor and the bottom.
As a 7yo, another student had me stick my head under there to look at the sliver of wood taped under the bottom edge of the thick wooden "skirt" of the alter. He said it was a piece of the cross.
With a 7yo head, I had to turn my head sideways to fit under there.
When I look back, I wonder who showed him.
Was quite the challenge to get my head under there. I wonder what an adult could do when a child is in that comprising position. Alone in a church. I doubt that was a piece of the cross too. Had me fooled for a long time.