The phone
The phone is mentioned throughout the film, but it doesn't seem to make any difference to the plot.
1 Right at the start, the Collingwoods are discussing their broken phone.
2 Later on, we find out that it's fixed when they ring the police.
3 The bad guys cut the phone line when they arrive. I don't understand why they do this, since this is before they find out that Mari lived there. Mr. Collingwood then says that the phone is broken anyway.
What was the need for all this?