Mr. Cuss the small town doctor visits the stranger out of curiosity. What odd thing does the stranger do?

The stranger exposes his invisible arm, refuses to acknowledge that it is invisible, and promptly nipped the doctor's nose with his finger and thumb.

"Something—exactly like a finger and thumb it felt—nipped my nose."
Bunting began to laugh.
"There wasn't anything there!" said Cuss, his voice running up into a shriek at the "there." "It's all very well for you to laugh, but I tell you I was so startled, I hit his cuff hard, and turned around, and cut out of the room—I left him—"
Cuss stopped. There was no mistaking the sincerity of his panic. He turned round in a helpless way and took a second glass of the excellent vicar's very inferior sherry. "When I hit his cuff," said Cuss, "I tell you, it felt exactly like hitting an arm. And there wasn't an arm! There wasn't the ghost of an arm!"