You might suspect that a healthy brain is smart enough to take notice of what you’ve eaten, but recent research shows it is easily fooled. Consider this ingenious experiment by Jeff Brunstrom at the University of Bristol. His subjects thought their task was simple: to eat a bowl of soup. Unbeknown to them, Brunstrom had hooked up a pipe that passed through the table and into the bowl, which allowed him to top-up some of his subjects’ soup without them noticing. He found that their later snacking depended almost entirely on the appearance of the bowl at the start of the meal – whether it seemed big or small – and very little on the actual amount he had fed them.