The suffering creature (if it was a suffering creature) was silent or dead.

Had chemical experiment accidentally injured some living thing?
Or--?
He recoiled from pursuing that second inquiry.

The laboratory had, by this time, become an object of horror to him.

He returned to the dwelling-house.
He put his hand on the latch of the gate, and looked back at the laboratory.

He hesitated.
That moaning cry, so piteous and so short-lived, haunted his ears.