The nitty gritty of this is:

In Krebs Cycle, Acetyl CoA binds to coenzyme A and the rest of the cycle of using and adding things can be done. But if there is Sodium Fluoroacetate present, it will bind to coenzyme A instead. The product of this is Fluorocitrate which binds to aconitase (another enzyme) so that the rest of Krebs Cycle cannot be done. This happens in the Mitochondria of cells. This process also produces Citrate, and this (plus fluorocitrate), in high enough amounts, also prevent the enzyme (phosphofructokinase-1) used in Glycolysis (step 1 of cellular respiration) from working, meaning not even the few ATP's from glycolysis can be made. SO cells have NO energy at all (4,5,6,7,8).

Along with this, other processes in the body stop working. Lactic Acidosis happens, where acid builds up in the blood lowering the pH (5). High amounts of citrate in the body is linked to heart failure, in some species it also effects the central nervous system. In carnivores, often respiratory failure (lungs) is what causes death during 1080 poisoning, and in herbivores it is often heart failure. Omnivores, tend to die from both cardiac (heart) or central nervous system disorders. (6,7,8)

The whole process of lethal poisoning can take 5-40 hours, but death is usually within 24 hours of ingestion (8).