A corpse is a dead monster, but there may be a way to revive it. Most annoyingly, the trolls and the Riders have the ability to revive themselves; that is, they will resurrect a few turns after they are killed. See their articles for strategies on how to prevent this and kill them permanently.
Most actions that try to dispose of a Rider corpse will instead instantly resurrect it. Among other actions, this includes teleporting it, tinning it, or taking it into your inventory. This resurrection is useful if you are Death farming.
You may also revive any corpse with turn undead, the spell or the wand. If you do this to a corpse in a bones file with a corpse on it, the ghost will inhabit it's original form and dissapear and the corpse will be revived.
In the following messages, substitute the names of the involved monsters for the monsters of your choice.
- Your <monster> corpse suddenly comes alive!
- You zapped yourself with a wand or spell of turn undead, and the <monster> corpse in your inventory came to life. The <monster> spawns adjacent to you. (Because the wand or spell hit you, the following message is often "You shudder in dread.")
- The <living monster>'s <monster> corpse suddenly comes alive!
- You zapped a monster with turn undead, and the <monster> corpse in its inventory came to life. The <monster> spawns adjacent to the <living monster>.
- A <monster> suddenly appears!
- This may indicate that you zapped an unseen monster with turn undead, and its <monster> corpse came to life where you can see it.
- <Player>'s ghost is suddenly drawn into its former body!
- You cast undead turning on a bones file corpse that had a ghost adjacent to it.
When a corpse revives itself, one of these messages may appear:
- A <monster> rises from the dead!
- This is the most common message; T monsters often will come back to life soon after death.
- You feel squirming in your backpack!
- Some corpse in your inventory (not being wielded) came to life. The monster will spawn adjacent to you. The message does not name the monster.
- The <monster> corpse writhes out of your grasp!
- You were wielding the <monster> corpse when it came to life. The <monster> spawns adjacent to you.
- Startled, the <living monster> drops a <monster> corpse as it revives!
- The <monster> will spawn adjacent to the <living monster>.
- An <monster> suddenly appears!
- This may indicate that an <monster> corpse, in the inventory of an unseen monster, came to life where you can see it.
- A <monster> writhes out of a sack in your pack!
- The player had a <monster> inside a sack as it returned from the dead.
- A <monster> writhes out of a sack!
- A <monster> corpse was in a sack as it came alive.
- A <monster> escapes from a <container>!
- A <monster> was dead in an unlocked container on the ground when it returned to life.
More interestingly, as other types of corpses rot, then mold may grow on them, and the corpse may revive as a mold. This typically produces the "rises from the dead" or "squirming in your backpack" message, as the corpse disappears and the mold spawns.