If you shoot an item frame with a crossbow that has a Piercing level of at least one, the arrow shot by that crossbow can pierce through the wall the item frame was placed on.
- Build a wall that is one block thick
- Place an item frame on that wall
- Shoot the item frame with an unenchanted crossbow
- The arrow doesn't pierce through the wall / disappears
- Replace the item frame with a new one
- Shoot the item frame with a crossbow that has at least Piercing I
- The arrow can pierce through the wall
As I was testing the crossbow I notice an odd glitch. I found out then when firing a crossbow with the piercing enchantment at a FULL glass block and an item frame on it the arrow will destroy the item frame as well as go through the glass block
Although this is a bug, it would be still cool as to keep as a feature as it can be used in many ways, mainly in secret doors.
A demonstration of this is: https://youtu.be/05IR4RXe2GQ
PS this was made in complete survival and void of texture packs or other things that can make stuff glitch or bug