In the previous episode the team started investigating the following enquiry, sent in to curiouscases@bbc.co.uk: "What determines left or right handedness and why are us lefties in the minority?"
They considered cockatoos, chimpanzees and Hannah's dog, Molly, to discover that humans are unique, with just one in ten of us being left-handed.
Today, they look inside the left-handed brain. Some researchers point to a link between left-handedness and impairments like autism or dyslexia. Others claim that lefties are more creative and artistic.
So what's the truth? The team consults Professors Sophie Scott, Chris McManus and Dorothy Bishop to find out.
Presenter: Adam Rutherford & Hannah Fry Producer: Michelle Martin.