How do you know when a squirrel is happy? Warning a predator? Protecting its food? Frustrated? The key to understanding their mood is not in their expressionless faces… it’s in their tail movements. Enter the research work of animal behaviorist Mikel Delgado, who wanted to know more about squirrel emotions and communications.

From her experiments, demonstrated in this episode of Deep Look, Delgado has come to wonder if frustration is a path to solving a problem with newly generated energy. Does frustration serve an evolutionary purpose?

“If you’re a squirrel and you’re trying to break into my bird feeder you could try to rip it open with your paws, you might start to chew,” said Delgado. “With all that energy, maybe by chance you accidentally knock the feeder. The idea is that between all these different attempts and the increased energy from being agitated, maybe that’s one way of solving the problem.”

In the archives: More squirrels, more emotions, more tails, more Deep Look, and a few animal behavior faves: Decoding the language of Prairie Dogs: America’s Meerkats, How to Speak Chimpanzee, More Evidence Birds Can Count, a wild crow solves a puzzle in 8 parts, and Why Do Cats Meow?