
The Len/Shutterstock.com (pig); kencameron/Getty Images (game controller)

Not all gamers are human. Researchers at Purdue University in Indiana recently trained four pigs to play a simple video game. The pigs learned to use their snouts to move a joystick. If they hit a target on the screen, they got a reward.
The study released earlier this year is the latest evidence of just how smart animals can be. Scientists don’t all agree on what makes an animal smart. But the ability to use tools, solve problems, and learn new skills are usually considered signs of intelligence. Here are some animals that scientists rank among the brainiest.