Why does Sinclair compare the actions of the women to the prestidigitator?

Sinclair's description illustrates the way the woman's actions can be compared to fine machinery..... quick, precise, and mechanically.

It was quite like the feat of a prestidigitator—for the woman worked so fast that the eye could literally not follow her, and there was only a mist of motion, and tangle after tangle of sausages appearing.