This genre of spades cannot be passed with perfect clearance.
This is the fact that Kevin insisted to keep when he wrote this scene. In his book, he explained that Lawrence wanted to get a perfect clearance for this genre, however, he failed to get the perfect clearance for spades genre.
Because that so called tip in the prompt to get perfect clearance is a lie.
The chemical Albert Arthington keep in his laboratory in the basement is the same chemical he mixed with the missile he released in the whole country.
If this chemical was fed directly to the organism, then the organism will wither and die slowly. However, the organism can continue to strive in an environment where there are humans, like this mansion that is plagued with dead human bodies.
Hence, the perfect clearance could not be obtained.
