Character mistake: Mia's Sea-Monkey, in a vertical position, was shown sinking to the bottom the jar. It isn't clear if the Sea-Monkey was dead or if Mia was referring to it when she said, "She's gonna freeze to death, Aiden", but Mia should have known how to properly care for her Sea-Monkey (or refer to the instructions) and, realizing the room was too cold, should have done something - such as wrapped a towel/blanket around the jar and/or moved the jar to a warmer location (e.g, near the fireplace). (01:22:33)
Character mistake: Shaft meets Junior for the first time and mocks him with the offer of bubbly water. Junior says "And as for that wedge of lime, it makes it alkaline, so..." It wouldn't, since lime juice is rather acidic. (00:23:10)
Character mistake: The Mother gave the Man (as Panda the cat) a bowl of vanilla ice cream with whipped cream and apparently some chocolate syrup. Chocolate is toxic to cats and most cats are lactose-intolerant. A mature/adult person should be aware that "people food", in general, is not healthy for cats and certain foods (chocolate and cow's milk) are particularly bad and possibly fatal. (00:27:27)
Suggested correction: This situation is actually more complicated in that the mother was seeing the man (her dead grandson), so wasn't really giving Panda the cat the ice cream. What can't be known is whether Panda as the man could eat ice cream with chocolate syrup and not get sick (e.g, vomit) after he turned back into a cat the same day.
Character mistake: Reina asked Cory if they could "do that thing" because it was helpful for her medical school training. Reina then put a raw slab of steak/meat across his forehead and made slits in the meat as well as jabbed at it. A medical student studying to become a brain surgeon should know about and practice the safe handling of raw meat. (00:23:10)
Character mistake: During her initial monologue, Katherine Newbury does the obligatory joke a 'foreign' host would make, rethorically asking where the good 'murican hosts are instead. Doing so, she mentions Martin Short, Jerry Seinfeld, Alec Baldwin. However, Martin Short is a bad example in the context of the joke, being Canadian-born.
Character mistake: At the start Smith takes a Krestal ballistic computer and barely holds it out to get wind speed. The proper technique is to hold it at arm's length into the wind.
Character mistake: Lucas says he loves "Ascension, rules, and anti-drug campaigns", so would not be likely to encourage Max to go to Soren's party after his father grounded him... or ask what his father would do about it (double-ground him?). Even though Lucas tells Max that he has "grown a lot" in the two hours after getting home and talking to his parents about all that happened that day (which they didn't believe), we aren't told in what way(s) he has grown - but it would not be favoring violation of rules. Also, Lucas later tells Hannah and Lily at Soren's house that he loves "Ascension, rules, anti-drug campaigns, and grilled cheese." This indicates that his view on rules has not changed, reinforcing the assertion that it was out of character for Lucas to encourage Max to go Soren's party while grounded.
Character mistake: When they're making the protection circle they make a star of David and not a pentagram, 6 points in a star vs 5 points.
Suggested correction: I don't think there was anything in the movie that dictated a pentagram had to be used. In the book of protection rituals they were using, the particular ritual showed a picture of the star of David they needed to create, so that's what they used (plus salt).
To add to the correction, what the mistake refers to as "Star of David" is a hexagram and the use of hexagrams in the occult are not uncommon. You can find salt protection circles that use the hexagram.
Character mistake: Nicolas Cage says "first battalion, tenth Marines from Camp Lejeune, North Carolina gunslingers signing out". It was the second Battalion 10th Marines that was called gunslingers, not the first.
Character mistake: Sabrina calls checkmate but the board is not actually in a checkmate position. (00:55:15)
Character mistake: A guidance counselor/principal told Calvin, "You're a very very smart young man. Perhaps even gifted. Last year you scored in the top ten percentile on the PSAT..." Because Calvin deliberately "blew" the SAT, the school official was going to make arrangements for Calvin to retake it. But this would not be necessary. The PSAT score (out of 1520) is considered equal to the SAT score (1600). The school official would be more helpful by getting Calvin admitted to college using the PSAT score. (00:08:35)