Minecraft wiki entry for Spawn_Egg, associated text: A spawn egg can be renamed on an anvil, and when used it spawns a mob with that name appearing over its head. The name can be seen only by aiming at the mob from four or fewer blocks away. This name also appears in death messages from the mob killing a player. If the player renames a spawn egg by the names described below, the mob appears described below. If the player renames a rabbit spawn egg "Toast", the secret skin of the rabbit appears when the egg is used. Naming a spawn egg "Dinnerbone" or "Grumm" causes the mob to appear upside down and show the given name above it. Renaming a vindicator "Johnny" causes it to act hostile to all mobs except for other illagers. Renaming a sheep "jeb_" makes the sheep's wool color cycle in a rainbow loop. This doesn't change the color of the wool you get from the sheep. Renaming a spawn egg of a hostile mob with an anvil and then spawning the hostile mob with the renamed spawn egg does not prevent the hostile mob from despawning, unlike using a name tag on the mob.