Egg

An egg in Nethack may be "just an egg" (presumably an ordinary unfertilised hen egg) or it may be the egg of a monster, in which case it will eventually hatch. For the purpose of conducts, eggs count as vegetarian but not vegan. Note that eating eggs can be dangerous. They may be rotten, in which case you will vomit, or on the later levels they may be cockatrice eggs, which will turn you to stone if you eat them. It is safer to leave eggs around as food for carnivorous pets. (Because eggs break when thrown, they cannot be used to tame dogs or cats.)

If you polymorph into a female egg-laying monster, you can lay an egg with the #sit command, and when it hatches it will become your pet. A randomly generated dragon egg will also become your pet if you are carrying it when it hatches. If you are male, there is a 50% chance that any egg which hatches while you are carrying it will become your pet. (From timeout.c, "The identity of one's father is learned, not innate.")

Cockatrice eggs are popular as projectiles that will petrify any stoning-susceptible monsters they hit. When you throw an egg, there is a risk that it will miss its target and go to waste, so you may prefer to wield the egg. If using cockatrice eggs that you have laid yourself, note that there is a Luck penalty for breaking your own eggs.