Chapter Seven: The Bite - S3-E7
Revealing mistake: When Joyce and Hop get out of the car at the fair, you can see Hopper's, Smirnoff's, and Joyce's breath as if it was cold out, despite being a July 4th fair. The grass looks dead as well. (00:30:20)
Revealing mistake: When Steve and Jonathan are climbing the radio tower, just before they reach the top, there is a wide shot, and if you look at Steve, you can see the far background around his body is swirling, revealing the shot to have been filmed in front of a green screen. (00:20:32)
Revealing mistake: When Bob and Joyce have lunch, Bob pops open a can of soda (which is period appropriate). The scene cuts to Joyce, then back to Bob. It is clear from how he is holding the can, and how he pretends to drink from it, that his newly opened soda is actually empty.
Answer: This is answered in a later episode so you should watch the entire season, but if you really want to know...SPOILERS She didn't, 1 (Vecna) killed all those children.
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