Nigori - Clearing up Cloudy Sake

In a perfect follow up to the pressing episode, Andy and Jim try to clear the water on a murky issue: nigori sake. What is it? WHY is it? How do they make it? And how should I drink it? Listen, and all the clouds will be lifted. Kanpai!
Vocab for this episode
Kassei nigori 活性にごり - “active” nigori sake with living yeast still making alcohol and, importantly, CO2. Can be explosive on opening.
Nigori にごり・濁り - Literally “cloudy.” Here, we’re talking about sake with visible rice residue. It can range from only slight cloudy to thick, creamy white.
Ori　おり・澱 - Lees, sediment, dregs… The very fine…