> The collision in a game is usually different from the visual polygons. This is because collision detection is relatively slow. A building with 10,000 visual polygons may have only 1,000 collision polygons. As a consequence, the map may have holes that you cannot see. This is what's going on when you fall through the map.

> This makes it very hard for the testers to test the collision on the map. During gta4, the testers found it particularly hard as characters could fall through the map depending on their animations and there was no way they could touch every bit on the map.

> This is why they asked for a rag doll gun. Alexander Roger created a special gun that instead of bullets would fire rag doll characters. The testers could go round the map and fire rag dolls at every building and hill side. --https://insiderockstarnorth.blogspot.com/2023/11/bugs-bugs-b...