Ellen's skis and straps change color from when she is at the lodge (33:30 min) and on the slopes (34:17 min) to the next scene where she removes her skis while tracking the Snowbeast (39:15 min).
Early in the movie, ski patroller Buster Smith goes out on his own to search for Jennifer a second time (against the wishes of his boss - Tony Rill). While out searching, Buster wipes out on the ski hill and as he falls, his hat and goggles and both skis come off. In the next scene as he is sliding/rolling down the hill, his hat miraculously reappears on his head and one ski becomes reattached. The following scene shows Buster hanging precariously over the edge of a drop with no hat or goggles (or skis) present as it should be.
When Tony is searching for Jennifer (the lost skier) going down the hill his jacket repeatedly goes from open to closed between shots.
The first close shot of the camper after it had been rolled onto its side shows the icicles hanging straight down, in the new direction of down, instead of sideways, consistent with the previous direction of down, indicating that between the two sequential shots, the camper had laid on its side at least overnight.
Several times during the film, when the Snowbeast is watching its next victim from the forest, it is suddenly shown in a different area. This is most noticeable when the sheriff and crew on snowmobiles, searching for the Snowbeast, say lets go back to the camper. The Snowbeast is near them when they say this. Suddenly its shown by the camper which is further away. Its never explained how the Snowbeast gets around so fast.
There doesn't appear to be a fireplace or pit in the barn that Gar and Ellen take refuge in for the night. They appear to burn wood on the open dirt floor for warmth. Exterior shots of the barn show no chimney nor any smoke that should be visible coming from the many cracks in the walls and probably from possible holes in the roof. Revealing that there is actually nothing burning inside this barn at anytime and the camp fire scenes are on a controlled stage set.
It appears that Sylvia Sidney took an unplanned fall during the gymnasium scene. She trips and falls pretty hard. It appears she may have broken an arm in the fall. She does not appear in the rest of the film despite being a major character earlier in the film.
Shadow of cameraman in some scenes.
Around the 38:00 when Ellen puts back on her ski googles, a crew member moving about can be seen from the reflective lenses.
Toward the end as "Gar" and "Ellen" are running out of the barn Bo Svenson bumps the antlers hanging above the door with his "weapon" and the antlers fall off and hit Yvette Mimieux right in the head. You can see her grab her head right before the cut.
At 49:26 Carrie is being placed in an ambulance while she asks Gar to tell Tony she's sorry for not stopping the Winter Carnival before lives were lost. (A nod to Jaws (1975)) (This could actually be a real ride for Sylvia after her hard fall in the prior scene). However, The ambulance attendants place Carrie into a darkened ambulance and then climb in the dark after her. This is not the procedure for EMT's/Attendants. They would need the interior lights on to care for the patient as they drive to the hospital.