One day, walking up the lane with the gun, and peeping over into the ploughed field, I saw a hare about sixty yards away.

The distance was too great to risk a shot, or rather it was preferable to wait for the chance of his coming nearer.
Stepping back gently behind the bushes, I watched him run to and fro, gradually approaching in a zig-zag line that must carry him right across in front.

I was positive that he had not seen me, and felt sure of bagging him; when suddenly--without any apparent cause--up went his head, he glanced round, and was off like the wind.
Yet there had not been the faintest noise, and I could not understand it, till all at once it occurred to me that it must be the scent.

The slight, scarcely perceptible, breeze blew in that direction: instantly he crossed the current from me he detected it and fled.

Afterwards I noticed that in the dusky twilight, if the wind is behind him, a hare will run straight at you as if about to deliberately charge your legs.
This incident by the ploughed field explained the failure of the wire.
Every other care had been taken, but we had forgotten to allow for the extreme delicacy of a wild animal's sense of smell.
In walking to the spot selected for the snare it is best to avoid even stepping on the run, and while setting it up to stand back as far as convenient and lean forward.