Chapter Eight: The Battle of Starcourt - S3-E8
Factual error: Because of the way radios work, when Suzie and Dustin are singing their duet they wouldn't be able to hear each other and the rest of the party would only hear a garbled mess. Per frequency only one radio should transmit at each time, so all the others can receive. If multiple radios are transmitting simultaneously, the signals will overlap and result in unintelligible noise. (00:35:53)
Chapter Eight: The Battle of Starcourt - S3-E8
Factual error: The value of Planck's constant used in the show, 6.62607004 is the value that was measured in 2014. The value that was in use in 1985 was 6.626176. The value was updated again in 2018, to 6.62607015.
Answer: The body was fake, made by the scientists at Hawkins Lab in an attempt to cover up his disappearance and the existence of the Upside Down.