“People can be given similar inputs yet interpret them in such different ways.”

How it works: ‘Your brain's best guess at reality’

Valerie Hazan, professor of speech sciences at University College London, told The Telegraph the riddle is not dissimilar from the Yanny-Laurel case, explaining “the signal is more ambiguous here, which may favour the more easy switching from one to the other”.

“The effect seems to work as follows: when you ‘think’ Green Needle you hear that word, but when you ‘think’ Brainstorm, you hear the other.

“Basically, you are priming your brain to expect acoustic patterns that match expected patterns for a particular word. When faced with an acoustic signal which is somewhat ambiguous because it is low-quality or noisy, your brain attempts a ‘best fit’ between what is heard and the expected word.

“If it expected patterns for Green Needle, then it will track the patterns in the signal which have more energy in higher frequencies as these are more consistent with some patterns in the sounds in Green Needle. If it expects Brainstorm, it will track the lower-frequency patterns which are more consistent with those you would find in a clearer production of Brainstorm.”