No one puts matches above doors by accident.

Whoever put it there must have meant it--and more than that, must have opened it and dropped one out inside the boot-box.
"Now," considered the astute Arthur, "it was pitch dark when Bickers was collared; lights were out, and the fellows thought they'd have a glim handy in case of need.

They struck one and spilt one, and shoved the box up there, in case they should want it again.

I say! what a clever chap I am! The tall chap this box belongs to did the job, eh ?" An expert might possibly find a flaw in this clue, but Arthur was a little proud of himself.
Next he spread out the sack and inspected the cord.

There was not much to help him here, one would suppose, and yet Arthur, being once on a good tack, thought it worth his while to look closely at these two relics.
The sack was not the ordinary type of potato-sack which most people associate with the term, but more like a large canvas pillow-case, such as some article of furniture might be packed in, or which might be used to envelop a small bath and its contents on a railway journey.