Cats don't have nine lives when it comes to venomous snakes, but they do have three. Dogs? Not so much. Scientists have now explained the striking difference between the chances of a cat and dog surviving a snake bite, and why sometimes no one should let the dogs out.

Dr Bryan Fry and Christina Zdenek of the University of Queensland were startled to learn only 31 percent of dogs survive being bitten by snakes in Australia, while the figure is 66 percent for cats. Since it takes more venom to kill a larger animal, it's natural to expect the reverse would be the case. “I’ve had two friends lose big dogs to snakebites, dying in less than 10 minutes even though the eastern brown snakes responsible were not particularly large specimens,” Fry said in a statement.

In Comparative Biochemistry and Physiology, Fry and Zdenek report the difference is in the blood. Naturally, the pair didn't want to test live animals' responses to venom. Instead, they exposed dog and cat blood in test tubes to venom from 11 snake species and found the dogs' blood clotted much faster than cats'.

That's important because many of Australia's most dangerous snakes kill by causing the blood of their victims to coagulate. Clotting is essential to prevent excessive bleeding after a wound. Some snakes' venoms use up all the molecules that cause clotting, so that there is nothing left to stop bleeding. This suggests dogs' naturally faster clotting blood makes them more vulnerable to these types of venoms.

Not all snake species use this approach – indeed Fry told IFLScience some do the exact opposite, preventing blood clots forming. However, venom-induced consumptive coagulopathy, as the approach is called, is particularly common among Australian snakes. Eastern brown snakes, which cause three times more bites to pets than the rest of Australia's plethora of venomous snake species combined, are masters of the art.

“All venoms acted faster on dog plasma than cat or human,” Zdenek said. “The spontaneous clotting time of the blood – even without venom – was dramatically faster in dogs than in cats.”

Fry told IFLScience humans lie somewhere between the two, “But closer to the cat end of the scale.” So far no other animals have been tested for comparison.

Canines also get bitten in more vulnerable places. “Dogs typically investigate with their nose and mouth, which are highly vascularized areas, whereas cats often swat with their paws,” Fry said.

Fry is skeptical the discovery will help us invent better treatments, for ourselves or our companions. Instead saying, “The anti-venoms are fine, the important thing is to get help very, very quickly. Vets must not delay [when treating dogs].”

The venoms in the study came from snakes that use consumptive coagulopathy around the world. Fry is keen to test how venoms based on entirely different principles, particularly those that prevent clotting, affect pet blood in comparison to our own.