Eating a monster egg (possibly after using some cooking system to prepare it) has a chance of giving you some intrinsics that the monster corpse can ordinarily confer.

A death ray zapped over a monster egg on the floor kills it, making it so that it will never hatch.

Possibly, this effect could also be achieved by erodeproofing or canceling the egg.

When a player is killed by a giant spider and leaves bones, there will be a web trap placed on their square, and occasionally one or two giant spider eggs.

Monsters that hatch from eggs should be specially flagged as being ineligible to death-drop items, since the only explanation would be that the item was with them in the egg, which makes no sense.

Awake (and non-paralyzed, etc) queen bees periodically lay a killer bee egg if there is not already one on their square, and their square is walkable terrain.

Oviparous monsters periodically lay eggs.

Archeologists begin the game able to recognize all eggs.

All eggs display their size, which is the same as their monster size (so e.g. an unidentified killer bee egg would be “tiny egg”). Non-monster eggs are small. Could also change the egg weight to match.

Antholes contain eggs of the type of ant the room is filled with; fewer than the ants themselves.

Generalize cockatrice-egg mechanics to all eggs: eggs of acidic monsters will be acidic, eggs of poisonous monsters will be poisonous. Possibly even have a (reduced) chance of getting intrinsics from a monster egg.

Queen bees drop a few killer bee eggs.

If you have egg on your face, your Charisma is temporarily and sharply reduced, lasting until either you get hit by or immersed in water or #wipe with a towel. This could also apply to having cream pie on your face.

A possible addition is for monsters to throw random (non-cockatrice) eggs at you.

Another possible addition is to add a new “egg trap”, which fires eggs at you with the intention of getting egg on you.

You can use stethoscopes (or possibly probing) on eggs to identify them.

When an egg gets very, very old, it cracks and releases a small stinking cloud. If it happens to be carried by the player, the cloud centers on the player. When it is close to rotten, the player can throw it and it will release the stinking cloud wherever it shatters. (The chance of it releasing a stinking cloud increases with age, asymptotically towards 100% the older the egg is).

Attempting to eat an old rotten egg will create the stinking cloud on the player’s square.

Randomized appearances for each type of egg.

Female oviparous monsters sometimes drop eggs of their species when killed. The chance is reduced if the monster was dead and revived.

Chicken eggs identify as such when you formally ID them, and all eggs of a known type stay identified for the rest of the game.

Easter eggs as an actual item, in addition to monster and chicken eggs. Possibly they have a chance of containing a candy bar, or a figurine.