Question

determined to force myself not to look at the painting but to undress quickly and get into bed. i began to undress, but in spite of every effort i could not keep myself from stealing a glance every now and then at the picture, and a glance was now sufficient to distress me. even when my back was turned to it, the idea of this strange face behind me, peering over my shoulder, was insufferable. i had grown nervous to a dismal degree. -the adventure of the mysterious picture, washington irving three best answers undressing uncomfortably going to sleep being unable to take his eyes away being nervous hearing the strange face make a noise done

Explanation:

The text describes the narrator's struggle to not look at a painting while undressing, and how just a glance at it distresses them. The idea of the face in the painting peering over their shoulder makes them extremely nervous. The key - elements are the inability to stop looking and the resulting nervousness.

Answer:

being unable to take his eyes away, being nervous