Character mistake: When interviewed by the police, Rosemary says "You do know where the arrow came from? It came from Mr Danvers' collection." But Lyle, the resident archery expert, would have his own collection of bows and arrows.
Other mistake: At the end, when a policeman pulls an arrow out of Franklin's shoulder, there's no sign of pain or blood, on the arrow or on Franklin's clothes.
Continuity mistake: Laura finds the missing bow in the church, and it has the string attached, but when the policeman holds it up, the string is missing.
Plot hole: When Rosemary discovers the side door to the church and a plastic knock, from an arrow, on the floor, she jumps to the conclusion that the arrow was shot from the side door. This all makes sense - this knowledge is how they catch Mr Danvers - but there are too many branches from the Yew tree to make this possible.
Continuity mistake: There are two things going on at once - Mr Danvers and the girls are at the Danvers house while the archery lesson is going on - but suddenly they merge, with Mr Danvers and the girls at the archery lesson, which, time wise, isn't possible.
Other mistake: When Malcolm is found dead with an arrow in his chest, the arrow is pointing down at an angle, which means it came from someone high up, but, later, we find out it came from someone of around the same height and standing on the ground, not high up on a ladder, or on a rooftop, which it should be, to get that angle.
Chosen answer: As far as hanging new wallpaper, there is no need to brush on any additional product once it has been pasted to the wall. It appears Helena may be doing an extra decorative step by applying a liquid glaze over the wallpaper to give it a more distinctive look, perhaps creating a sheen effect on the surface. Glaze can also be tinted to give a muted colored tone. It could also be a protective sealant. However, to remove old wallpaper, a product is brushed on that dissolves the old paste so the paper can be easily scraped off.
raywest ★