Poirot smiled.

"Mon ami, have you ever, when writing a letter, been arrested by
the fact that you did not know how to spell a certain word?"

"Yes, often. I suppose every one has."

"Exactly. And have you not, in such a case, tried the word once
or twice on the edge of the blotting-paper, or a spare scrap of
paper, to see if it looked right? Well, that is what Mrs.
Inglethorp did. You will notice that the word 'possessed' is
spelt first with one 's' and subsequently with two--correctly. To
make sure, she had further tried it in a sentence, thus: 'I am
possessed.' Now, what did that tell me? It told me that Mrs.
Inglethorp had been writing the word 'possessed' that afternoon,
and, having the fragment of paper found in the grate fresh in my
mind, the possibility of a will--(a document almost certain to
contain that word)--occurred to me at once. This possibility was
confirmed by a further circumstance. In the general confusion,
the boudoir had not been swept that morning, and near the desk
were several traces of brown mould and earth. The weather had
been perfectly fine for some days, and no ordinary boots would
have left such a heavy deposit.

"I strolled to the window, and saw at once that the begonia beds
had been newly planted. The mould in the beds was exactly
similar to that on the floor of the boudoir, and also I learnt
from you that they had been planted yesterday afternoon. I was
now sure that one, or possibly both of the gardeners--for there