Don’t try to wrong a raven, not even once. It’s not going to forget and it’s probably going to shun you for a long time.

When it comes to animal personalities, there are dogs, which are loyal and usually love you no matter what. And on the other side are ravens, who are only too happy to remember what you look like and ostracize you, according to a study published this week in the journal Animal Behavior. The researchers trained nine ravens by hand for the purpose of testing — or, really, taunting — them to see if these birds could tell fair from unfair. Spoiler alert: They can. They will bear a grudge, and this is what makes these bitter corvids birds after my own heart.

These nine ravens were raised in captivity, growing to become familiar with the researchers. Then came the test.

The ravens were put in a cage along with two trainers on each one. The first trainer gave the raven a piece of bread. The raven then carried the bread to the other trainer on the other side, and exchanged it for cheese.

The second time, the raven was soundly rejected. Instead of getting the cheese, it had to watch as the trainer just ate the cheese in front of it.

Two days later, the researcher rounded up up seven of the birds and presented them with three trainers: the fair one who gave them the bread, the unfair one who ate food in front of them, and a neutral one. Six out of seven birds chose the fair one. One chose the neutral one. Nobody wanted to play with the mean one.

One month later, they tested all nine birds. This time, seven chose the fair trainer and only one chose the unfair one. Study co-author Jorg Massen, a post-doc at the University of Vienna, told National Geographic that the ravens might be even less forgiving than this study suggests. He thinks they might remember for as long as two years, which is how long they’re capable of remembering who was in a cage with them.

In some ways, this finding isn’t terribly surprising since ravens are known for being very smart (they even hold funerals) and have a complex social structure. To succeed in any type of group interaction, you need to remember who’s good to you and who you need to plot revenge on. So be careful next time you’re walking in the park and want to throw a rock at a raven. We’ve long been warned what kind of damage birds can do.