Chapter One: The Vanishing of Will Byers - S1-E1
Continuity mistake: When Will is being chased by the monster and runs into his garage, he pulls down his .22 rifle hanging on a wall rack. After he loads a few rounds aiming it at the door, the monster appears behind him. After Will and the monster disappear, the scene shows his rifle is back on the wall rack in its original spot. Did Will or the monster place it back on the wall rack while Will was being abducted? (00:07:25 - 00:08:10)
Chapter Three: Holly, Jolly - S1-E3
Continuity mistake: When Mrs. Wheeler bursts through the door, angry with Nancy about lying to the police she throws her purse down. When they get to the kitchen she throws the same purse down again.
Chapter Four: The Body - S1-E4
Continuity mistake: Right after Nancy puts together the torn photo of Barb at the pool it cuts to Dr. Brennan and crew in hazmat suits. At the beginning of the shot when they try to reach Shepard on the comms, the digital clock reads 6:54:08. After Brennan says "Try him again.", the shot has the clock blurred in the background as 6:40 something, and a bit later it reads 6:40:55. (00:27:20 - 00:27:54)
Chapter Six: The Monster - S1-E6
Continuity mistake: Eleven is in the shop and stealing eggos. As the freezer door shuts she walks away holding three boxes. The next shot of her walking towards the exit she is holding four.
Chapter Seven: The Bathtub - S1-E7
Continuity mistake: When Mike and Lucas notice a van pulling out of a side street and coming to them, the sky is blue, but in the next shot, it is orange. (00:04:03)
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.