Episode 2 of “Stranger Things” is also when Dustin (Gaten Matarazzo), Lucas (Caleb McLaughlin) and Mike (Finn Wolfhard) try to figure out what Eleven knows about Will. (Netflix)

The obsessive fandom around Netflix’s ’80s era sci-fi thriller “Stranger Things” began, for most viewers, after they watched the second episode, according to a report by the streaming network. For those familiar with the Upside Down, that basically means people had to find out: What happened to Barb?

Expanding on similar research from last year, Netflix examined viewing behavior for 30 popular original and licensed series to identify the “hooked episode” — the first installment that led at least 70 percent of viewers who watched that episode to complete the entire first season of a show. Here’s a promotional explainer from Bill Nye (who probably hopes people will become hooked on his forthcoming Netflix talk show.)

This year, Netflix analyzed viewership across multiple continents — more than 35 countries in total — and found that people throughout the world tended to get invested in shows at around the same episode.

There are a few caveats, of course: Not all shows are available in all countries. And the research doesn’t say anything about how many people watched these shows since Netflix doesn’t share viewership numbers. (Ted Sarandos, president of the streaming service, has said that ratings aren’t a particularly useful metric since Netflix doesn’t sell advertising.) The streaming service has also declined to confirm estimates by outside sources including Nielsen and Symphony Advanced Media.

Among the interesting tidbits in Netflix’s “hooked” data: Viewers of Aziz Ansari’s “Master of None” were sold on the comedy after episode four, which focused on racism in Hollywood. The first season of Ryan Murphy’s anthology series “American Horror Story” also won over viewers by the fourth episode, which featured the ominous return of two former residents of the so-called Murder House. The CW show “Jane the Virgin,” which typically includes more than 20 episodes per season, found a dedicated following after the seventh episode. And Netflix says the tipping point in “Making a Murderer” arrived at the fourth episode, when Steven Avery’s nephew Brendan Dassey is introduced as a new suspect and controversially interrogated by police.

We can make a few guesses as to why some of the “hooked” episodes persuaded viewers to stick with a show. The fourth episode of “American Horror Story” ends on a haunting cliffhanger, and Chapter 7, as it’s known on “Jane the Virgin,” is when the show’s epic love triangle went into hyperdrive. Rory and Dean-shippers will understand why “Gilmore Girls” clinched its fan base during episode seven, which marks the couple’s first kiss.

Here’s more data from Netflix on when shows such as “The Get Down,” “Grey’s Anatomy” and “Fuller House” persuaded viewers to finish the entire first season.

Netflix released a report on which episodes of popular shows nab a fan following. (Netflix)