Dogs can learn words like treat and walk, but can they tell what we’re feeling just by looking at our faces? A new study suggests they can!

In previous studies, scientists learned that dogs can tell the difference between two big human emotions—happiness and anger—when we smile or frown. You could call these opposite emotions. One is positive, or pleasant, and the other is negative, or unpleasant. But can dogs tell the difference between two negative emotions, like anger and fear? The new study aimed to find out.

For the study, scientists at the University of Vienna in Austria used a machine called an MRI scanner to produce images of the brains of 14 dogs, including border collies, a Labrador retriever, and a golden retriever. They had to train the dogs to stay perfectly still while the machine did its work.

First, scientists showed the dogs human faces that were either happy or neutral (not showing any expression) while the machine scanned the dogs’ brains. The happy faces activated, or made active, parts of the brain that respond to rewards.

“This [activation] is related when the dog is expecting a snack or a food reward, but also when they hear praise,” scientist Laura Cuaya told the Washington Post.

Then scientists showed the dogs faces that were sad, angry, or fearful. The dogs’ brains could not tell the difference between sadness and anger on a person’s face. But they could tell the difference between anger and fear. This probably means dogs use other clues besides facial expressions to tell when people are sad versus angry.

The scientists say the dogs in the study showed their brains can understand more about human facial expressions than previously thought. 

Click through the slideshow for more photos of the scientists and dogs!