Continuity mistake: When Venom starts tossing Kasady around in his cell, Eddie right hand is positioned in the rightmost space of the door. Kasady bites him when his arm is through the space to the left of that, though. His arm is also pointed at a different angle and height between shots. (00:29:35)
Revealing mistake: Kasady squishes a spider that is walking on the postcard. The splattered blotch, strictly divided in red and black, is disproportionately large for the size of the insect. (00:25:35)
Other mistake: When Eddie reads Kasady's letter, it's obvious that the whole speech can't fit inside the postcard. Moreover, parts of it don't even make sense since Eddie could never "see" the part about Shriek; he knows nothing about her at that point of the movie. Finally, either way when we see him read the letter, the parts shown don't match the narration; for instance when he gets to the part about Kasady's heart stopping, it is on the part of the postcard opposite of the one he's 'reading'. (00:24:25)
Continuity mistake: Eddie meets Anne at L'Araignee ("The Spider") and hugs her. His hand is at the top of her shoulder, middle of the back, top of the shoulder again. (00:18:45)
Continuity mistake: Venom is drawing hyper-fast parts of the material they ogled on the wall of Kasady's cell. On Eddy's messy desk there's a sheet with data from California State University, very recognizable for the colors and shape of the graph. When they draw the tree, notice that the sheet turns 90° multiple times between shots without Venom touching it. (00:10:50)
Audio problem: It is well-established that the symbiote can communicate with Eddie telepathically and others do not hear it. However, it can also speak normally and does so plenty of times; when the two are arguing in the bathroom of the prison, we see that Venom opens its mouth and move its 'lips', which would mean the woman in the stall and Detective Mulligan can hear him - which makes no sense in the scene. (00:06:30)
Revealing mistake: In a random act of road rage, Carnage sticks out a couple of tentacles, effortlessly lifts up a truck that was driving by, and tosses it off the bridge. Great, but no matter how strong Carnage and each tentacle of his is, it can't nullify physics; it lifts that vehicle stopping entirely its momentum, and Carnage's car does not even remotely budge for the added weight. (00:45:25)
Audio problem: Eddie Brock is trying to find where Carnage might be headed. To draw inspiration he listens to the recording of the last time they spoke (when incidentally he was never seen retrieving the tape). However, the lines in the recording are different takes from the original scene, spoken at a brisker pace without dramatic acting pauses. (00:38:00 - 00:42:40)
Other mistake: Eddie witnesses in horror from the window his former alien partner wrecking his Ducati bike in the alley below. Venom exits stage right and possesses a lady riding a bicycle, headed towards his right. Somehow, this double *right* turn leads to Eddie witnessing Venom's middle finger from a window to the *left* of his original position. (00:34:30)
Other mistake: In the comics it is always very clear that the clothes Venom and Carnage appear to be wearing are shapes the symbiotes take and not actual clothes. In the movie, Eddie wears his own clothes, and so does Kasady, since we literally see him stealing the flamboyant outfit from some guy, and the clothes stay solid even when the symbiote is incapacitated. In that case, it makes no sense that the clothes at no point get damaged when they get stabbed or even torn open like it often happens in the movie.
Other mistake: Kasady kills Dr. Pazzo hanging/strangling her with one of his tentacles coming from above. When you look at the section Frances was held in though, and considering the moderate speed the tentacles showed in their slithering while on camera, there's no way they could have reached her in time - that without mentioning the fact that Kasady himself appears inside the cell with no explanation - if he was already there by hacking, it does not explain the movement in foreground at the beginning of the scene.
Other mistake: Dr. Pazzo (which literally means "Dr. Mad" in Italian, incidentally) turns towards the computer with the voice synthesizer before the phrase is spoken. (00:51:20)
Other mistake: In the end credits, Christopher Godwin is credited as "Headmaster (1997). " The scene when he appears had as caption "St. Estes Reform School - California 1996."
Revealing mistake: Shriek's scream is strong enough to cause the explosion of a helicopter at great distance, but the frame of the windshield is unscathed. (00:54:15)
Other mistake: When Casady crushes Shriek's cell, they both have their hands on the glass wall that gets shattered, nothing protects them, and yet she has her hands all over him to passionately make out - the shattered glass is like it never existed. (00:52:30)
Plot hole: It is of course possible that Eddie Brock heard nothing at all about the biggest news in the whole city and State if he did not turn the TV, check the phone or computer for about 24 hours. But there has been a manhunt for Kasady for that long of a time and nobody including the police checked on the one man Kasady is trying to kill, and who was chilling at home all along. Also, obviously the "breaking news" moment is not breaking nor news. (00:40:25)
Factual error: When we see Young Shriek struggling with Young Detective Mulligan, the gunshot explodes when the weapon is pointed up and at distance from her face. Obviously a direct shot to her eye socket would have killed her, but she is blind in that eye and has a scar in two distinct parts of the socket. It's hard to imagine how a wound with that pattern could have occurred even thinking of the bullet ricocheting off the top of the trunk or something. (00:02:55)
Continuity mistake: When Carnage steals the Mustang he is driving through the financial district in San Francisco. It then cuts to him driving into the city on the Bay Bridge. How and why did he go from being in the city to leaving and driving back in?
Continuity mistake: Eddie snoops around the park of Cletus' old delinquent kids' home. He brandishes the torch with his left hand, but when he walks in a frame later he's holding it in his right hand. (00:00:48)
Other mistake: In a weird move concocted for the movie, Carnage creates a tornado spinning around real fast with his tentacle sticking out. Against physics, one of the tentacles gets a hold of the prison chief and keep still for a few seconds while Carnage's body in the background has spun around itself a few times already. (00:38:30)
Answer: If they conducted a one-on-one interview, Eddie might've risked sharing some personal things to get Cletus to open up more. Eddie also took her leaving pretty hard. He might be one of those people who, you spend five minutes talking to them and they're GOING to bring up their ex.
Captain Defenestrator