I was going to post some fun facts about QUB3D but got side tracked
... anywhere here's Bad Apple on QUB3D
(fun facts to come later)

I briefly thought that rockstar had a unused cutscene variant of a velum approach to Cayo.
But no, it's just that no sane person goes into Cayo aggressive so I had literally never seen this until now.
So maybe you also haven't seen this before :p

In a Last Dose cutscene there is a bit where the lights go out and the characters are only briefly illuminated by gunshots
Rather amusingly, the mocap actors actually held the poses instead of just freezing it and you can see them trying to stay still when the lights are on.

the game deciding if you should get softlocked trying to join a casino heist or not
also when going through the mantrap
also when just existing in the game in general

Also fun to see the characters as they walk off which isn't normally visible.
Passing the bottle and shaking it before being turned into stone in T Pose

The last shot of this cutscene actually takes place over the road... because movie magic.

GTA 5 has a rather advanced audio system.
One of the interesting bits is the game has the means to synthesize sounds in real time, which is used quite often.
Including for ambient dubstep as shown here in a 2014 talk by Alistair MacGregor

bro i just want to join up some casino heists but im just getting sent to the dungeon

Or more sensationally:
EXCLUSIVE LOOK AT GTA 6 CLOTHING FOR FIRST TIME OUTSIDE THE LEAKED FOOTAGE?!??!!111/?!