It's not dumb as a brick. There are 1 Int creatures, and even they have some intelligence. It's a standard animal intelligence - it can toss stuff at you if you annoy it, just like any big animal can do.
Here, Rhinos have a 2 Int in the MM, and here is a real life one tossing a warthog:
The person you were responding to was discussing the Tarrasque throwing things like rocks at foes. Moving a creature with a horn attack (i.e. melee attack with forced movement included) is very very different than picking up a rock and throwing it at that creature. When you post a video of a rhino tossing a rock at the warthog, then your Int 3 argument holds more water. As is, apples and oranges between the two (or in your terminology, a strawman since throwing a creature as part of a melee attack was not the other poster's claim).
At the level of animal intelligence where creatures consistently throw objects at other creatures, one is more at the Ape level (Int 6) or Baboon (Int 4). No doubt a Tarrasque could throw things and has the physical tools to do so, it just wouldn't be SOP for such a creature since he has no fellow creatures of his own species to emulate. Most attacking creatures would not use thrown weapons against it (arrows, bolts, and spells are not thrown). For the vast majority of creatures it would ever face, any of them using thrown weapons would be so close that they would quickly die.
Learning tends to be done via emulation with low intelligence creatures and sorry, the Tarrasque typically just doesn't have any role models for throwing things at foes.
Grabbing foes? Sure. Lot's of Int 0 creatures grab things for food.
Throwing an object if not trying to hit a target with the object? Possibly.
Shoving a foe? Unlikely, but if it really wanted the foe away from it, sure.
It's assumed the DM is capable of using the general rules for all things, monsters and PCs. Improvised weapons are part of the rules. So are the shove and grapple action for instance, neither of which are in most monster writeups either. You're not a slave to the write-up, since particularly in this edition the authors give the DM a range of additional tools which are used where appropriate for any encounter.
Agreed.
I would actually, but I am replying to someone who says he goes strictly by the write-up, and strictly by the write-up he can't. And if he is flexible enough to expand beyond the write-up for dropping alchemist fire, then it's fair game to use the improvised ranged attack in response. You don't get it both ways - you can't apply to strict-write-up when it benefits your position, and then flexibility outside the write-up when that pleases you. Either we're strict, or not. He has to pick one.
It's fair game, but again, an Int 3 creature tends to not be the brightest bulb on the planet. To learn how to throw objects at targets, it would need some creature to show it how to do so first. Repeatedly. IMO. Any given DM can feel free to have a Tarrasque stand on its head too, but I wouldn't have it do such a trick either.
Throwing an object at something is levels of intelligence above just randomly throwing something.
With regard to Elephants have Int 3 in the book (someone else brought this up), that's just bad research. Elephants have one of the best non-human brains on the planet due to size, mass, and neuron complexity. Elephants should easily be Int 5 or 6.
Elephant cognition