Despite the apparent simplicity of picking numbers at random, it is virtually impossible to produce a sequence of truly random numbers. Although numbers seem to pop-up spontaneously in one's mind, their choice is invariably influenced by previously generated numbers . Here, we demonstrate how the eyes and their position give an insight into the nature of the systematic choices made by the brain's ‘random number generator’. By measuring a person's vertical and horizontal eye position, we were able to predict with reliable confidence the size of the next number — before it was spoken. Specifically, a leftward and downward change in eye position announced that the next number would be smaller than the last. Correspondingly, if the eyes changed position to the right and upward, it forecast that the next number would be larger. Apart from supporting the old wisdom that it is often the eyes that betray the mind, the findings highlight the intricate links between supposedly abstract thought processes, the body's actions and the world around us.