Cats are mysterious critters. Unlike dogs, they seem indifferent to our presence, even though research shows that they really do love us. But how can we tell what they really have on their minds?

Researchers from the U.K.'s University of Lincoln may have finally unlocked that mystery. For their study, the team evaluated 29 cats living in an animal shelter in Canada. Using a computer program called CatFACS (Facial Action Coding System,) they were able to analyze the changes in facial expressions that cats displayed both in presence of humans and away from them.

According to the study, which was published in the journal Behavioural Processes, cats basically have three moods: engaged, afraid or angry. You probably already know what your cat looks like when she's mad — her ears are flat and she's likely hissing or growling. She may also lick her nose, drop her jaw, meow loudly or stretch her mouth open wide.

When they are afraid, cats may blink or half-blink excessively. So that sideways glance your cat gives you sometimes may not mean he thinks you're stupid (although he probably does.) It may also mean that he is afraid. Interestingly, cats may also tilt their heads and look at things to the left when they're afraid, whereas the same gesture with a head tilt and gaze to the right might signal a more relaxed demeanor.

Of course, this study was based on a small sample of cats living in an animal shelter. The researchers concede that the facial expressions of a cat living in her forever home might be different from those of cats living in a rescue center. But the study does take an interesting glimpse into the moods of our cats as well as what is going on underneath those sweet furry faces.