Research shows that, by age three, children understand that imaginary objects do not come to life. This is especially clear with respect to everyday objects ─ children know that even though they imagine a pencil in an empty box, the box will remain empty. However, emotion can sometimes disrupt this understanding, or at least its expression. That is, even though a child knows that monsters are not real, the thought of a monster under a bed might be enough to make a child refuse to go into his room at night. Indeed, research shows that children have a more difficult time displaying their understanding of the causal relations between imagination and reality when they are asked to pretend or imagine scary things, like monsters. In one study, preschool children were shown an empty box and were asked to imagine a monster inside. All children agreed that the box was empty. However, when they were left alone with the box they exhibited fear and avoidance of it.