I have plenty of friends from all over the English speaking world. Because I know where they are from, and what they sound like, I have become quite familiar with the nuances of each variety of English. By hearing someone speak and then comparing it to the way my friends talk, I can almost always deduce a person’s origins.
While this usually freaks out random South Africans in train stations or Mancs mums at Disneyland, I’ve never been able to speak in each accent as the narrator of this video does. Of course he doesn’t really attempt a Tyneside or Brummie accent but it’s good enough for the range he puts forth.