Paediatrician Guddi Singh looks at how children begin to become independent, with Professor Elisabeth Hill testing newly crawling babies with an optical illusion made of Perspex that looks like a sheer, vertical drop. Dr Emily Jones visits 18-month-old Amaya and attaches sensors to her to monitor the physiological changes in her body during a tantrum, while Professor Usha Goswami attaches young babies to highly sensitive brain scanners to see how the infants respond to different types of speech. Last in the series.