Closing your eyes when trying to recall events increases the chances of accuracy, researchers at the University of Surrey suggest. Scientists tested people's ability to remember details of films showing fake crime scenes. They hope the studies will help witnesses recall details more accurately when questioned by police.

A whistling language like that quoted in "Tree of Codes," she said, speaks to "how we humans adapt to and interact with our environment, not being separate, but really being in a merged relationship with everything around us." That positive attitude sets Ms. Lim apart from some of the other musical-linguistic ventures.

It's sometimes said that the eyes are windows into the soul, revealing deep emotions that we might otherwise want to hide. Although modern science precludes the existence of the soul, it does suggest that there is a kernel of truth in this old saying: it turns out the eyes not only reflect what is happening in the brain but may also influence how we remember things and make decisions.

This story is part of BBC Future's "Best of 2015" list, our greatest hits of the year. Browse the full list. - Thomas Ormerod's team of security officers faced a seemingly impossible task. At airports across Europe, they were asked to interview passengers on their history and travel plans.