After training fruit flies to avoid a new smell at a specific intensity, the researchers offered them a choice between that dangerous odour level and a weaker one. The flies did well when the safe option was four or five times weaker, but chose randomly if the difference was only 10%.

Crucially, as the differences became smaller and trickier to distinguish, the flies took more and more time to make a decision, waiting much longer in an intermediate zone between the two odour levels.

This is a pattern that psychologists have studied for many decades. “The same mathematical models that describe human decision-making also capture the flies’ behaviour perfectly,” Prof Miesenböck told BBC News. “That’s remarkable.”