A longer yawn may correlate to a bigger brain size, according to a new study which also found that the animals with bigger brain are more variable in the length of their yawns.
Researchers from the State University of New York in the US looked at the videos of 29 mammals yawning to calculate the average length of their yawns.
The animals had their brain weight already documented in an earlier research.
When the researchers crunched the numbers, they realised that brain weight and the number of neurons in the outer layer of the brain called cortex can reliably predict yawn length.
For instance, gorillas, horses, walruses and African elephants may have huge sizes but they have shorter yawns than humans because the size of their brains are smaller compared with ours.
The findings suggest that the length of yawn does not correlate to the size of the body but to the size of the brain, 'Tech Times' reported.
The research team led by Andrew Gallup, from the State University of New York also found that the animals with bigger brain were more variable in the length of their yawns.
According to Liz Cirulli Rogers, from Duke University School of Medicine, it is possible that more intelligent animals have different types of yawn in response to different stimuli while the less-intelligent ones only have one type of yawn.
"We show that both the mean and variance in yawn duration are robust predictors of mammalian brain weight and cortical neuron number," Gallup added.