You can hear them on the video!
"By placing cameras inside the hive, the researchers discovered that the signal often happens when a bee bumps into another bee near the accelerometer, and not when bees are waggle dancing or exchanging food.
?We suggest that, in the majority of instances, it is bees being startled that produce the signal,? says Bencsik. The team propose that instead of the ?stop? signal, it should be called the ?whooping? signal."
https://www.newscientist.com/article/2121275-honeybees-let-out-a-whoop-when-they-bump-into-each-other/
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