The narrator likely smirks (line 46) because:

do you have more to the question?

the illustration   that would give a reader a clear understanding of the text is a picture of men constructing the frame of a building.the frame is made of iron bars. the text describes the job of blacksmiths'. these were very organised and they had different names: "the driver" and "the heater". the text describes the way in which these men worked ; they worked iron pieces as if they were playing a sport. in fact, the text wants to show the men's skills. the text also puts some emphasis on the use of '' rivets'' in construction. this kind of nails were not always used in the construction of manhattan.

some examples:

"and with an underhand toss he hurled the smoking rivet straight at the catcher, who caught it in mid-air in his catching can." men's skills

"when the driver was ready for a new " the emphasis on the rivet ( special nail used in construction).

" it against a beam to remove any cinders, and jammed it into the waiting hole. " the emphasis on the rivet.

the figurative meanings of these lines are questioning the tyger's strength and beauty. the meaning contributes to the overall message of them poem because it is explaining how strong the tyger is.

now just elaborate off of that. : )