I've somewhat mixed feeling about this ep. Mike starts explaining in good, simple and easy to follow way and then just drops it :( He just needed to continue in similar fashion. Like, one can point from artist_table to genre_table and back but in order to preserve many-to-many nature of data one would have to have multiple copies same data at each side and leave behind the uniqueness of keys and then to change, for example, artists name one would have to change in multiple records at once and queries would have to filter through a lot more data  and so on... it would be terribly inefficient and wasteful but it would work... and it would be obvious to listener why this is a bad design... and in an effort to improve it one can evolve it to have third intermediate table...
"believe me this is bad" will not cut for explanation :(
*sigh*
sorry, I guess I'm ranting..