Rats

"A third of the world’s food supply is consumed or destroyed by rats. ... There are more rodents currently infected with plague in North America ... than there were in Europe at the time of the Black Death."

"‘Rats that survive to the age of four are the wisest and the most cynical beasts on earth,’ an exterminator told Mitchell sixty years ago. ‘A trap means nothing to them, no matter how skilfully set. They just kick it around until it snaps; then they eat the bait. And they can detect poisoned bait a yard off. I believe some of them can read.’ "

If you love reading about rats, then this is the link for you.