You have only to lean it against a certain point in a man's anatomy, lunge ever so little and the whole thing is done.

Come here, Mr.Ledsam, and I will show you the exact spot." Francis made no movement.

His eyes were fixed upon the weapon.
"If I had only known!" he muttered.
"My dear fellow, if you had," the other protested soothingly, "you know perfectly well that it would not have made the slightest difference.
Perhaps that little break in your voice would not have come quite so naturally, the little sweep of your arm towards me, the man whom a moment's thoughtlessness might sweep into Eternity, would have been a little stiffer, but what matter?
You would still have done your best and you would probably still have succeeded.

You don't care about trifling with Eternity, eh?
Very well, I will find the place for you." Hilditch's fingers strayed along his shirt-front until he found a certain spot.

Then he leaned the dagger against it, his forefinger and second finger pressed against the hilt.