Explain this quote: “It is this,” I answered producing at trowel from beneath the folds of my roquelaire.” where it falls in the...

Montresor pulls the trowel from his cloak after Fortunato
expresses his shock at Montresor's insistence that he is a member of a masonic society. 
Of course, Montresor really means that he is a mason in the sense of it being a name for
someone involved in stone work; Montresor shows the trowel as a symbol of his intendion
to use his masonry skills in order to entomb Fortunato in the recesses of the catacomb. 
Montresor did not realize that Fortunato was actually not referring to the masonic
society at all.  Had Fortunato been more sober, he would probably have wondered why
Montresor carried a trowel; of course, Fortunato's drunkenness prevented him from
recognizing Montresor's hints on more than one occasion.