Rats have been blamed for spreading a deadly disease called the Plague for hundreds of years but now scientists think that gerbils were actually to blame.
The Plague, also known as the Black Death, killed millions of people across Europe in the 14th century.
It was spread by tiny insects, called fleas, and up until now experts thought those fleas were carried by rats.
But now scientists in Norway believe the blame lies with gerbils from Asia.
Watch Martin's report here to find out more.
But if you've got a pet gerbil don't worry. You can't get the Plague from modern gerbils and what's more the disease is incredibly rare and easily treatable now.