Why are Nigerians swapping their high-value banknotes?

Nigerians have to swap their current high-value banknotes for new ones by the end of January. Why the change?Also, we take a rare look at the workings of an elite Somali military unit fighting Al Shabab.Plus, from Harare - President Mnangagwa makes this year's state of the nation address in Zimbabwe's new parliamentary building.More on those stories in this podcast with Audrey Brown