i have completed the game 3 times now and i still haave not seen thoes damn rat things. WHERE ARE THEY.
In vanilla STALKER you will find most of them at Lab X18 after returning. For instance if you take on the Kill the Bloodsucker task in Dark Valley after returning to Sid from X18 they will be swarming the place, along with Bloodsuckers. The Bloodsucker you need kill in that task is roaming SE of there though. Many of the mods that add mutant spawning, typically the ones that add mutants that were cut from the game, will have lots of Tuskanos (rats).