Continuity mistake: When Constantine manages to get the mirror through the window he falls on his back. To the right on the screen a chair lies on the floor beside a dresser. A few shots later when it cuts to Constantine getting up we can see the chair has changed position as its back now covers the opening of the dresser. (00:08:15)
Factual error: When Angela is watching the security video on her laptop of her sister committing suicide, you can see she's playing it using Quicktime. She rewinds a couple of seconds by clicking on the first button of the video player. Actually, when you click this button, it takes you to the beginning of the video. The second button would have rewound it a short time. (00:25:20)
Continuity mistake: In the pool when Constantine grabs the possessed Angela, he grabs her by her head with both hands. When it cuts he's holding onto her shoulders. (01:26:40)
Continuity mistake: When Constantine gives Baltazar the final punch you can see Baltazar's tie lying on his chest. When it cuts from behind him his tie is over his shoulder. In the next shot it's back on his chest. (01:10:55)
Continuity mistake: Constantine catches a spider under a glass and blows some smoke in it. The amount of smoke in the glass differs between shots. (00:33:25)
Continuity mistake: In the scene where John commits suicide by slitting his wrist, the soles of his shoes go from brand new and unmarked (quite clearly seen in a couple of close up shots) to scuffed and worn (also seen quite well in a couple of shots). (01:34:25)
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 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 Lucifer lights Constantine's smoke he has his left arm down, then he closes the Zippo and it cuts. Now his left arm is up. (01:37:05)
Continuity mistake: There is a close up shot, when John slits his wrist, of the blood seeping around his watch. It is an integral part of the scene, yet moments later, when viewed from above, the blood is nowhere near the watch.
Factual error: Rachel Weisz fires approximately 29 shots from her semi-automatic handgun without reloading - vastly more shots than her gun can hold.
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 Constantine gives Angela Isabel's name tag, Angela is holding the tag so that half the tag is between her fingers and the rest of the half inside her hand. When it cuts half the tag is still between her fingers but the rest of the half is now outside her fist. (00:44:30)
Continuity mistake: When Constantine gets thrown into the glass paned door at the end just before he slashes his wrists, every time it cuts to the scene showing the door the broken glass left in the door is always in a different pattern. (01:32:55)
Continuity mistake: When Father Hennessy stabs himself with the cork opener the items around him change position between the shots. (00:47:55)
Continuity mistake: When Angela visits Constantine you can see an ash tray and two bottles along with other stuff on Constantine's table. Later, when the demons fly outside Constantine's window, as the camera moves over the table you can see all items has suddenly been removed from the table. (00:34:40 - 00:36:10)
Continuity mistake: After Constantine has thrown the holy water at Baltazar you can see Baltazar stretching out both hands to grab Constantine. When it cuts, Baltazar grabs Constantine by his throat with only one hand . (01:09:55)
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 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)
Continuity mistake: When Constantine is seeing the doctor about his cancer you can see the lights on the screen showing the X-rays are on. When it cuts after she says "This is aggressive", the lights are suddenly off. (00:14:15)
Answer: Sin for a good reason is still sin, and as Gabriel says earlier, you can't buy your way into Heaven. Real Catholic dogma, however, doesn't hold the mentally ill as condemned for committing suicide.
Greg Dwyer
Except Isabel wasn't mentally ill. She saw angels and demons just like Constantine did. It was her parents who believed she was mentally ill.
While suicide is a mortal sin, it's shown later (as in major plot point) that sacrificing yourself to save the world is a redeeming act.
Yes, but Constantine also said "My parents were normal. They did what most parents would do. They made it worse. You think you're crazy long enough, you find a way out" which could relate to Isabel losing her sanity in a way as well because of her family and how they saw her. The whole Isabel's sacrifice is added by the novelization but the movie is ambiguous about the suicide.
mp1920
Except Isabel wasn't mentally ill. She saw half breeds just like John did.
Sacrificing yourself for others isn't a sin.