When the boys are on the snow-covered roof, something gets Laughing Gravy's attention and he walks off the set-up out of camera range. After a brief cutaway to Charlie Hall, he's back right next to the boys.
The snow and flower pots on Charlie Hall's window sill aren't consistent from shot to shot. He throws a flower pot at Ollie, leaving three, but in a following long shot, four are on the windowsill.
As Oliver is packing the suitcase, the collars and box on the mantel change places between shots of Stanley. (This could be intentional.)
After Stan has pulled the dog up in the sheet and closed the window, Ollie shouts 'Hey'. From behind, he has both hands to his mouth, but only one from the front.
The snow and especially the stalactites hanging from the roof are obviously fake.