Minecraft wiki entry for Mob_grinder, associated text: Projectiles that can be picked up again by the player after lodging in a block (i.e. arrows and tridents) also have the ability to hit mobs if they are moved after becoming lodged. The total number of hits a projectile can inflict before becoming inert and impossible to retrieve depends on its type and the piercing enchantment: a normal arrow can hit one mob; arrows shot by piercing-enchanted crossbows can hit (enchantment level + 1) mobs; and tridents can hit an infinite number of mobs.[1] Hits inflicted by moving the projectile after it has been lodged in a block count as hits for the player who launched the projectile, even hours later and/or while the player is no longer nearby. Such hits cause the the mob to drop experience and player-kill loot as long as the player who launched the projectile is loaded somewhere in the world. In addition, the loot dropped is subject to the looting buff if the player holds a looting sword in the main hand at the time the kill occurs.