Jays react angrily when shown a cup-and-balls-style magic trick in which their favourite snack is swapped for a less appealing one. Their responses show cognitive abilities that may come into play when they pilfer food caches hidden by other birds. Eurasian jays (Garrulus glandarius) have impressive memories and show some capacity for imagining the beliefs and intentions of others, known as theory of mind. As such, Alexandra Schnell and her colleagues at the University of Cambridge wondered whether jays would be sensitive to cognitive illusions designed to fool humans. First, they tested six birds to find out which food each one preferred from a choice of worms, cheese and peanuts.