Continuity mistake: In the beginning when the Mexican's foot goes through the planks under the sand, a lot of dust comes up. When it cuts from within the hole we can see through it and the amount of dust has decreased. (00:01:00)
Continuity mistake: When the Mexican steps his foot through the planks making the hole in the ground, we can see from inside the hole that he is standing directly above it. When it cuts we get a close-up view of the hole outside but the Mexican isn't above it, he is moving closer to it. (00:01:10)
Continuity mistake: When the Mexican is reaching down the hole for The Spear of Destiny we can see him turning his head to the side. When it cuts he is looking down the hole. Also when he reach his hand down his arm goes between a broken plank and the edge of the hole. When it cuts his arm has moved over the broken plank. (00:01:15)
Continuity mistake: When the Mexican picks up the Spear of Destiny, his grip on it changes between the shots. (00:01:35)
Continuity mistake: When the Mexican wraps up the Spear of Destiny he places the Nazi flag with the swastika pointing up. A couple of shots later when the Mexican turns around, the flag is folded in a different way and the Swastika is not visible. (00:01:35)
Continuity mistake: When the Mexican is about to get up he holds onto the Spear of Destiny with both hands. When it cuts it's in his right hand only. (00:01:45)
Continuity mistake: When the Mexican walks away his friends talks to him while crouching. When it cuts we see his friend in the background but now he is on his knees. (00:01:50)
Continuity mistake: In the beginning when the woman takes the pot out of the oven and is about to pour the hot water into the cup, she places her left hand on the table beside the cup. When it cuts to a close-up her hand is gone. (00:02:45)
Continuity mistake: In the beginning when the woman is about to pour hot water in to her cup we can see a spoon on the tray. When it cuts the spoon has changed position, and also a piece of paper has appeared on the tray. (00:02:45)
Continuity mistake: In the beginning before Constantine gets out of the taxi, he drops a cigarette out of the window. The size of the cigarette differs between the shots. (00:03:25)
Continuity mistake: When Constantine approaches the apartments where the possessed girl is, he meets a woman holding a man while walking in front of him. When it cuts the woman is still holding the man, but now she is behind him. (00:04:20)
Continuity mistake: When the possessed girl talks to Constantine she has a big lump of hair on her forehead. When it cuts there is no trace of hair on her forehead. (00:05:25)
Continuity mistake: When Constantine places the medallion on the possessed girl's head she starts screaming and waving her hands. When it cuts to a close-up of her we can see her hand is still. In the next shot she waves her hands again. (00:05:30)
Continuity mistake: During the exorcism scene Constantine says "I need a mirror, now. At least 3 feet high.", while holding his left arm down. When it cuts to him shouting "Move." his left arm is up. (00:06:10)
Continuity mistake: When we see Chas in his car the first time he lifts his right arm to adjust the mirror. When it cuts you can see he is adjusting it with his left hand. (00:06:25)
Continuity mistake: When Chas is in his car talking to his mirror you see him holding his right hand on the steering wheel. When Constantine calls for him it cuts and you see Chas resting his arm on the seat beside him instead. (00:06:40)
Continuity mistake: When the mirror has been brought and Constantine tells them to tie the cord to it we can see one of them tying it. When Constantine says "Close your eyes" it cuts and we can see the man has suddenly stopped tying the cord and is now holding onto the mirror. (00:07:15)
Continuity mistake: When Constantine is preaching over the possessed girl it cuts to a close-up of the chubby Thai man, we can see the man standing beside him has his head turned to right. His head change from being turned to right to left between the shots. (00:07:25)
Continuity mistake: When the demon climbs out of the possessed and gets stuck in the mirror we see the reflection of the girl in the mirror and she is smiling with her eyes closed. When it cuts to a close-up of her she is smiling with her eyes open. It cuts again and we see in the mirror she is smiling with her eyes shut. (00:07:50)
Continuity mistake: When Constantine pulls the rope attached to the mirror the distance between his hands on the rope change several times between the shots. (00:08:05)
Chosen answer: According to the legend of "The Spear", it is indestructible.
Nick Bylsma