It surprised Mary, watching his fumbling fingers.

She decided that Jack must be even younger than he looked.
She noticed also that the boy cast, from time to time, a sharp, rather worried glance of expectation toward the door, as if he feared it would open and disclose some important arrival.

Furthermore, those old worn shirts hanging on the wall were much too large for the throat and shoulders of Jack.
Apparently, he lived there with some companion, and a companion of such a nature that he did not wish him to be seen by visitors.

This explained the lad's coldness in receiving a guest; it also stimulated Mary to linger about a few more minutes..