Minecraft wiki entry for Traps, associated text: Target springs secondary trap and is forced into 1x1 shaft.
Target triggers tripwire whilst falling down shaft.
Target hits cobweb at bottom.
Piston placed in Step 8 triggers, pushing Block of Netherite directly above hole.
Repeater clock triggered, causing pistons placed in Steps 7 and 10 to repeatedly shift the Blocks of Netherite back and forth, preventing them from being dug out. Blocks of Netherite are shifted at an interval of time that is shorter than the amount of time needed to break a Block of Netherite by conventional means such as by pickaxe.
Target is contained within the trap until trap is disabled or target dies (or remains trapped indefinetly if difficulty settings forbid death by hunger and target has no other means of commiting suicide (Ender pearls, Potions etc.)).