Video - Should have & 3rd conditional

Rob must have eaten Dan's cake! Dan was looking forward to eating a piece of cake he'd brought into the BBC. But when he looked for it in the fridge, it was gone. He's sure Rob took it because he's done that before. How do you use modal verbs in the past to express that idea? Dan has a 90-second lesson to explain all. For more, visit our website: http://www.bbc.co.uk/learningenglish/english/course/upper-intermediate/unit-25/session-1