Stupidity: David was seriously injured by Olivia a few times (e.g, hit by her car and on the head with a baseball bat). When Olivia went into the bedroom, David was able to knock over his chair, get a knife off the floor, and free himself from being duct-taped to the chair. David took the car keys but left the knife on the floor, even though he was weak and vulnerable and Olivia had previously chased and caught him. When David returned to the cabin, Olivia came in with the knife and keys. (01:02:55 - 01:09:49)
Stupidity: Two oil rig workers were looking at two young ladies in bikinis who were sunning themselves on a boat/yacht. One oil rig worker said, "That's where we should be right now. With them, enjoying the sun, instead of baking in it." Both men had double layers on - a jacket or sweater over a jersey or T-shirt - and one man was wearing a tossel cap. Even if it gets cold on the rigs at night, they did not need to be dressed in warm attire during the sunny daylight hours. (00:10:35)
Stupidity: Grace (?) came out of hiding holding a fire extinguisher upside-down as though prepared to use the fire extinguisher to whack any Allosaurus that approached her. Actually spraying the dinosaur's eyes with the chemical contents of the fire extinguisher - and from a greater distance by using the hose - would have been much more practical and effective as a repellent and thereby less likely to result in getting maimed/killed. (She did not use the fire extinguisher at all). (01:02:20)
Stupidity: Sam slid under the truck to narrowly escape the lioness. Even though there was more than enough ground clearance, the lioness did not go under the truck to attack Sam, as though the truck's frame were a barrier. The lioness could have easily crawled under the truck (unless a CGI lioness is not as spry or nimble as a "real" lioness). Sam being under the truck would not constitute adequate protection from an attacking lioness. (01:10:30 - 01:35:20)
Stupidity: The location of the small hole near the bottom of the wood-trimmed wall where Everette passed Sharyn a note and pencil would have taken much more time and effort to accomplish compared to merely penetrating the wall a little higher (where there would not have been wood trimming/baseboard on both sides). (00:10:00)
Stupidity: One of the major reveals and plot twists of the movie lies in the fact that a certain character is an accomplice of the medium. The reveal, though, does not explain at all how said individual managed to fool Poirot; the trick briefly shown involves a simple rope pull to open a door. Poirot was looking exactly for that kind of trick, paces around the room constantly on maximum alert, and examines the door itself later. Likewise, it does not explain where and how they could hide the stuffed animal.
Stupidity: The cleaning crew can't open doors and stand in front of a large window. They see a couple walking a dog, so they scream, "Hey!" and wave their hands in the air, even though the people are not looking their way. They do not bang on the glass or use their flashlights to try to draw attention. (00:29:13)
Stupidity: Ben passes out on the living room floor. Before Jack leaves, he places a lantern-type flashlight a couple of inches above Ben's right shoulder. Apparently, Ben's first move when he wakes up in total darkness is to move his right hand from alongside his body to behind his shoulder, where he just happens to find the flashlight. Even if Ben's first reaction is to feel for a head injury, his hand does not go high enough to bump into the flashlight. (00:02:12 - 00:02:40)
Stupidity: Simi sets the wooden tepee structure on fire with Claudia next to it, and Claudia's clothes get engulfed in flames. Claudia continues to stand next to the fire, flailing her arms instead of following the commonly-known "learn not to burn" procedure that is taught to children: "Stop, drop, and roll" to extinguish the fire on one's clothes - and to stay away from fire. (01:31:00)
Stupidity: Milton, straddling Edie's body on the floor, is about to pull the plastic sheeting over her head. Edie's eyes suddenly open, and she starts screaming. Instead of quickly pulling the plastic sheeting over her head and suffocating her, Milton half-heartedly struggles to control Edie's hands, which she somehow manages to raise from alongside her body and around his to be in front of her neck. (00:38:50)
