Not everyone who hears a dog growling assumes they are being threatened.

Researchers at Eötvös Loránd University in Hungary tested whether people can identify the context of a dog’s growl. They used three different natural situations: dogs at play, dogs guarding food, and dogs faced with a stranger. Participants were able to identify the contexts for the growling at levels higher than chance, although they had a more difficult time distinguishing growls for guarding food and threatening a stranger. The article was published in May 2017 in the Royal Society Open Science journal.

Previous studies have suggested people have more difficulty differentiating between playful and threatening growls. The researchers hypothesized that the length of the growls in those studies, which were restricted to 1.2 seconds, caused confusion as that is shorter than an average aggressive growl and longer than an average playful growl.

As a result, this study aimed to give the context of natural growling situations without modifying the frequency or time of the growls. Researchers used 10 second sections from original recordings to play for participants and had eight different growl samples for each of the three contexts. From the available samples, they created 20 different sets consisting of 6 samples, and each set was used for two listeners.

There were 40 participants, 14 men and 26 women. For the first set of growls, they received a scoring sheet for emotional scaling, choosing from five inner states: aggression, fear, despair, happiness, and playfulness. Rather than just choosing the emotion, however, they had a visual analogue scale and placed the mark along a line, allowing them to rate how strongly the growl associated with a particular emotion.

For the second set of growls the participant listened to, participants received a context recognition sheet, and identified whether the growls were from food guarding, playing, or threatening a stranger.

In the results from the emotional scaling, participants associated playfulness and happiness with the play growling and lower levels of aggression. Aggression was rated for both food guarding and threatening a stranger, but was rated the highest for food guarding.

Results for context recognition showed that participants classified 81% of the play growls correctly, 60% of the food guarding correctly, and 50% of the threatening growls correctly. The reason for the lower numbers for the more aggressive growls is that listeners had a hard time distinguishing the two—the most common error was to identify the threatening a stranger growl as a food guarding growl.

While the participants’ demographics had no effect on how they scored the growls emotionally, women and dog owners were more likely to correctly recognize the context of growls. Because these results differ from previous studies, the researchers concluded that the length and rhythm of the growls likely helped the listeners to correctly identify growls.

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