When Duncan stops to see if he can help Sindy, he looks in the mirror and sees her unzip her outer garments to show off her red top (and, presumably, what's inside), but when she gets to the window, the purple vest she is wearing under her outer coat is zipped all the way to the top.
Between the 4th and 5th minutes of the movie, during the poolside assassination, Hilde's makeup changes from pink eye shadow near both eyes to pink eye shadow in the form of a lightning bolt near her right eye.
When the gang led by Hilde kills the fat man in Austin, blood splashes all over their faces and clothes. Yet Sindy ,standing right next to them, has no stains at all on her.
At around 45 minutes the fat man kicks over the food trays but the trays are still there between shots.
At around 1 hour 39 minutes when the head goes through the window,the window is still intact in the next shot.
When Duncan is looking into his cabin using the thermal camera, he can see through the windows like the glass wouldn't be there. This is not how thermal camera works, as it would only show the temperature of the window glass and not through it. If the thermal vision would show through the window, it would do so through the walls, too.
The owl is obviously a captive owl, as the noise it makes are 'baby' sounds which young owls make when begging for food. Mature owls that have grown up in the wild do not make this noise as they have learned to hunt for their prey and do not have a need to beg for food.
In the high end motel early in the movie, someone pulls a clear bottle of alcohol from an ice bucket. There are no labels on the bottle, which is extremely unlikely in a high end hotel where name brand is at a premium.
While photographing the owl it flies away making the sound of flapping wings. Owls possess silent flight capabilities.
Vivian says "He's currently staking out in Belarus, Russia", to Duncan while discussing business at the restaurant. Belarus and Russia are two separate countries.
The phone number at the Antique Mall sign, which appears on the scene after entering Triple Oak, Montana, has the area code of Toronto, Canada (905), not Montana (406).
At the beginning of the film a house is shown in Villa La Angostura, Chile, but Villa La Angostura is in Argentina.
When Duncan teaching about countries at the school one girl asks "Do they eat turkey in Turkey?". Duncan answers "No, chicken. And the put them on skewers." But usually lamb puts skewer not chicken and that's name is Turkish Kebab.
In the Netflix version, from around 18:50, the sun goes down in the wrong direction, right - left.
If this is the North hemisphere, it should move left to right.
(If you use a sunrise sequence to imitate sunset, it is not enough to play it in reverse: you also need to mirror left to right.)