Continuity mistake: When Nancy throws her mother's bottle to the floor she throws it bottom first. When it cuts the bottle lands on its side. With the velocity the bottle was thrown it would have landed bottom first. (00:51:40)
Continuity mistake: Nancy and Glen are talking on a bridge and Nancy is holding a book. Glen then takes it from her and reads it's title aloud, and in a closeup he is holding the book closed. But as the shot changes Glen is holding the book so that it is open. (00:53:05)
Continuity mistake: Nancy comes home and there are regular bars on the windows. When she gets to the front door, they change to a heart shaped design. (00:55:55)
Continuity mistake: When Johnny Depp is talking on the phone with Heather, he lifts his bedroom's curtain in order to see her (since they live right across the street), pushing it up to his right. But when they hang up, he pulls the curtain back from his left. (00:59:10 - 01:00:50)
Continuity mistake: After Nancy pulls her phone out in frustration, she wraps the phone cord around it, and places it on her bed nice and neatly. But in the next shot of the phone mysteriously ringing, the phone is in a different position and the phone cord is wrapped around the phone differently. (01:03:50)
Continuity mistake: When Nancy is at her bedroom window, she says "OK Krueger, we play in your court" and she is holding her alarm clock. She then pulls down the blind, then when it cuts to inside, Nancy is walking over to her bed but isn't holding her alarm clock. If you look, the clock is on her bedside table, but she doesn't put it there. (01:11:25)
Continuity mistake: Nancy rigs a lamp to explode. However, the one she rigged isn't the one that exploded. It's a completely different lamp. (01:12:20 - 01:22:30)
Continuity mistake: In Nancy's final showdown dream, she goes down to the cellar, then goes to open the door which leads to the boiler room. When she opens the door it's hinged on her right hand side, yet when the shot changes the door is now hinged on her left hand side. (01:13:25)
Continuity mistake: Eventually Nancy goes to sleep in her short-sleeved gown. But when she sets the alarm to her wristwatch, she's wearing a long-sleeve sweater. (01:14:40)
Continuity mistake: In the boiler room Nancy finds Glenn's bloody headphones. As she raises them up from the ground, between shots, the way she holds them changes. (01:16:30)
Continuity mistake: When Freddy falls down the stairs there is an umbrella lying down by the door. The umbrella moves between the shots. (01:18:55)
Continuity mistake: When Freddy is set alight, he runs up the cellar staircase which has steps with no backs to them. Then when he is hit by the door and rolls down the stairs, the staircase has changed, and the backs of the steps are there. (01:19:50)
Continuity mistake: When Nancy is in the boiler room towards the end of the movie, Freddy suddenly jumps out and scares her. In this shot Freddy is wearing his hat. Earlier in the movie Nancy took the hat from him. After the shot where Freddy jumps out at her with his hat on, the next scene shows him chasing her down a staircase without his hat. (01:20:09)
Continuity mistake: When Krueger smashes his arms out the front door window, large pieces of glass are still hanging in the window, but in the next shot, as he pulls Nancy's mother through, all the glass has disappeared. (01:25:10)
Continuity mistake: At the end of the film the two girls holding the skipping rope chanting the Freddy rhyme swap sides between shots. (01:25:10)
Continuity mistake: Keep watching when Glen sneaks through Nancy's bedroom window for the lighting in the bedroom. When the exterior shots are shown the light is always on but it is sometimes off inside.
Continuity mistake: In the bath scene, Nancy is falling asleep and is awoken by her mother then starts falling back to sleep and her inflatable pillow is roughly 8 inches above her head. When the shot changes to face her, the pillow is now below her head.
Continuity mistake: Just before Nancy goes into her final confrontational dream she sets the countdown on her wristwatch. The closeups are of a chunky watch with a thick strap, but in the long shots she is wearing a dainty pink ladies watch.
Continuity mistake: When Glenn dies, the blood pours up from his bed. It's seen splashing directly onto the lamp above, though in the next shot after his mother walks in, the lamp has shifted and is completely clean.
Continuity mistake: After Nancy wakes up from her final dream that draws Freddy out, the coffee pot behind her is full of coffee. When Freddy jumps from behind the bed, Nancy runs to a now empty coffee pot and smashes it on Freddy's head.
Answer: The scene you are referring to is a dream sequence. In dreams everything is different and how they change throughout the movie is no mistake.
SAZOO1975