Mechanical rat traps are one possible alternative to poisons; another alternative is to buy a cat, although cats capable of dealing with rats are relatively rare; in many cultures, hunting dogs have been used instead. Both of these methods have a disadvantage of being comparatively messy, a particular problem when the building with a rat problem is to be uninhabited for some months. Anticoagulants have the advantage that their first effect is dehydration from blood loss, causing the unfortunate rodent to leave the building in search of water.

Newer rodenticides have been developed to work with by reducing the sperm count in males to deprive them of the ability to procreate rather than to kill rodents outright. They are usually administered in the breeding seasons of most rodents.

ABOUT THOSE SERINE PROTEASES:

Clotting factors are identified by number and the serine proteases (also called K-dependent factors for reasons which are about to become clear) are factors II, VII, IX, and X. These factors are produced in an inactive state by the liver and go happily circulating through the bloodstream awaiting activation. When a vessel tears and it becomes necessary to form a clot, these factors are activated in a process that requires Vitamin K (a fat soluble vitamin not as famous as its fat-soluble cousins Vitamins A and E). As the clotting factors are activated, Vitamin K is inactivated but later recycled by another set of enzymes to be ready to participate in clotting factor activation again later.

As long as there is plenty of Vitamin K, the serine proteases can be activated and clotting can proceed normally.

The anticoagulant rodenticides abolish Vitamin K recycling. This means that as soon as one’s active Vitamin K reserves are depleted, there can be no meaningful blood clotting.

In cases of poisoning one would expect symptoms to be nearly immediate but in the case of anticoagulant rodenticide poisoning, it takes several days to deplete Vitamin K. After that, even the smallest of jostles and traumas can lead to life-threatening bleeds.