may baffle some Brits, but it actually has an easy and obvious answer that should only require a few seconds of thought. This riddle is an example of a rebus , symbol or set of words that represents another word, phrase or syllable. More of a rebus clue call them 'frame games' or 'word picture puzzles'.

This particular clue from the US National Institute of Environmental Health Sciences (NIH) asks people to complete the phrase from the words “head” and “heels”. What phrase can you come up with that uses these words? See the answer below.

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For the answer to this rebus clue, all you need to do is think about what word could be added to the words you can already see to make it make sense. In this case, you only need to think of the phrase “head over heels”. Similar clues like this show the letters “VA” next to “vaders”. A large gap is shown between the words as an extra clue for the final answer, which is “space invaders”.

The NIH used above was designed for children and it can be used to help them with their development. Nicole M. Avena, PhD, assistant professor of neuroscience at the Mount Sinai School of Medicine in New York City and visiting professor of health psychology at Princeton University said: “While some studies show that brain training games are not effective, the recollection and work that the brain does during these games keeps your mind fresh and alert… Brain functions that you practise during these games—and the repetition of them—can help improve response time and sharpness.” He added that some games work differently for people and finding your own challenge might be the best thing to do. "If you think about diet and exercise routines, some things work better for some people than others, and the same is true with brain games,” he said. It is not clear if brain games and teasers really improve your cognitive abilities, but they can help to keep you relaxed and fresh, leading to indirect benefits.

Why not try something a little more tricky? You can try to Or, see whether you have a 'highly intelligent mind' by.