What causes cat bites to be poisonous?
Cat bites are not poisonous. Any animal bite, if left untreated, can cause infection.
When dealing with spider bites it is very important to know if it is a poisonous species of spider or not. It is very helpful to know what types of spiders are poisonous in the area where you are bitten. One should clean the bite, apply ice and elevate the area. Bites from poisonous spiders should be seen by a medical professional immediately.
There are any number of causes of death in cats. Old age Disease (cancer, diabetes, kidney failure, etc.) Infection Accident Malnutrition Parasites Poisoning Abuse A previous answer mentioned the eating of poisonous geckos. Please note that geckos themselves aren't poisonous to the cat, but carry a parasitic liver fluke that can cause a fatal condition in the cat.