Cavemen should be particularly good at tracking monsters to eat them, so they should get one of the following:
An artifact rock of detect ants, which conveys warning of all a-class monsters (or possibly only ants) when carried. If it enters your inventory and there are ants on the level, or you enter a new level containing ants when the previous level had none, you get a message “You feel antsy”. There are corresponding messages “You feel less antsy” for when you no longer detect any ants.
When a monster drinks a cursed potion of invisibility and you feel aggravated at it, you should additionally gain detection of that specific monster for some time (or just permanently, since monster invisibility doesn’t wear off).
All bane-type artifacts which don’t already give warning of the monster type they are a bane of, should give warning of those monsters.
New artifact Apiarist’s Veil, a cloth hat, perhaps an elven helm or fedora, that gives warning of all insects and pacifies nearby bees.
New artifact Regicider (or Regicide, Usurper or Royalbane): a sword of some type that isn’t already overrepresented in artifacts that has bonuses and warns to monsters with the M2_LORD and/or M2_PRINCE flags. Maybe it would also work on demon lords, depending on if they are considered nobility, or just overlords.
On a somewhat sillier note its attributes could also extend to queen bees and also have some ability to detect royal jelly on the map (invoke effect?)
Demonbane, while wielded, warns of demons.
