The He imp would alight on the rail, about ten feet in front of her, and pretend to be very sick, squawking feebly and drooping his black wings with a struggling flutter, as if it was all he could do to keep his perch.

The cat, her narrow eyes opening very wide, would start to creep up to him.

The She imp would then alight on the rail behind her and nip her sharply by the tail, and go hopping clumsily off down the rail.

The cat would wheel with an angry _pfiff-ff_, and start after this new quarry.

Whereupon the He imp would again nip her tail.
This would be repeated several times before the cat would realize that she was being made a fool of.