OK, on wikipedia, it says:
"There are creatures that lack certain ability scores (undead, for example, have no constitution). These are called nonabilities and affect how that creature is treated by certain spells and effects. The aforementioned undead, for example, are immune to almost anything that requires a Fortitude save, unless it can also affect objects. This is not the same as having a score of zero (which causes death, paralysis or unconsciousness depending on the ability in question)."
Is this true? If so, which abilities cause death/paralysis/unconsciousness?