Q3A is totally made up of cool shit. Singling out particular objects or fixtures in maps is a difficult thing to do. A single bleeding head, or a chained zombie body, or a large organ of some primordial alien creature is handing around at unlikely places. I looked everywhere in the 26 default maps that comes with q3a. I even looked deep into the lava pools, became a spectator and went to those unlikely places, and here is a list of everything I found apart from the run of the mill skull torches and 8-layered moving light fixtures.
In q3dm15 (Demon Keep), down by the lava pool and going back to the main area via the passageway below the BFG, there is this head all alone in the corner. This has to be some programmer. The pool of blood is animated, and the eyes fade between having pupils and not having pupils.
This is just a light fixture from q3tourney1...
...gets a little more interesting from her point of view
This is a weird body chained to the wall on one side of q3tourney3. The intenstines are static and probably rotten, but the rest of the blood in the body is actually flowing through it! You have to stand on a ledge and zoom in to get a good view.
This is from q3tourney4, a part of the structure has a skull and a ribcage floating around in the goo.
Right at the bottom of the water pool in q3dm8, there is this skeleton lying around, to remind players not to stay submersed too long. Spend a little time in the water, and you will notice how the view warps inside water.
What in fucking hell is this thing? Found in two maps, this is from q3dm9.
This one is really cool. You end up here, and you get a message like "you have entered a secret area." I think this is the only place in the game where this happens. This is in q3dm11. You get a 50 health in here (shhh!!!) and dopefish! (ssshhh!!!!).
This is one of the two gigantic creatures whose mouths have been torn off and attached to the arena. This is from q3dm13. Notice how the metal rods are used to keep the mouth open. Stare at it, and you can see it undulating. They should have added some saliva.
The entire q3dm14 map has a eerie flesh beneath the metal/concrete thing going on. All the spawn points for weapons are like that. There are also these reptilian claws/gargantuan plant spikes jutting out over the lava, like it has broken through the wall.
q3dm5 is a really good map for playing with 3-4 people. Not surprisingly, it is called the forgotten place, and it really is, even if you are a regular player, start this map up and you'll know why. The barrels here are pretty cool.
They inflict damage if you stand on them.
q3dm7, aka temple of retribution aka temple of redistribution for those who could not pronounce retribution has a bunch of really cool dead bodies lying around. Near the lava, there are these skulls on sticks to start off...
Then lying around in a godforsaken corner is this poor ex-arena player's skeleton - or maybe its just kept there for kicks...
...and everyone's favorite, this zombie body near the red armour place.
Dont tell me who this is, but its half a larger than life statue embedded in a gothic wall... that's some art ideas for real life - disembodied larger than life statues would be soooo cool on MY cieling.
And in a tiny place on The arena of remorse, there is a friggin mirror on the top... why? to make sure your hair is alright?
The other animal mouth in q3a, this one is in q3dm1 and everyone must know about this because this level was in the demo. Look at how the tongue has actually smashed through the floor and hit on the lava. Those are the kind of touches that makes quake a great game.
In q3dm2 (notice the wharf-like quality of the map?) under the floorboords of where you get the plasma gun, are a whole bunch of cast away skeletons. You will have to crouch to look though - and no time for that when some fragging is going on.
To finish, these are trunks of what appear to be enourmous boas digesting some heavy duty meat. Stare at them in q3dm4, and you will see them undulating exactly like food was travelling down them. You can't miss them, but you probably will miss the movement.
I hope I have not overlooked something...