More advanced hacks add squirrel sprites that run up trees when the player approaches, similar to the wild Pokémon rustling in Fire Red ’s Safari Zone. This requires scripting movement and collision detection.
: Nintendo released an updated v1.1 of FireRed that fixed minor bugs, but this update shifted many internal memory addresses. Because the "Squirrels" version is based on v1.0, using a v1.1 ROM with a v1.0 patch will often cause the game to crash or fail to load.
