It was a ferret.
The silence was broken by Rupert Grant.

He spoke in that sweet and steely voice which he reserved for great occasions and practised for hours together in his bedroom.

He said: "Mr Montmorency, I think ?" The old gentleman started, lifted his eyes with a bland bewilderment, picked up the ferret by the neck, stuffed it alive into his trousers pocket, smiled apologetically, and said: "Sir." "You are a house-agent, are you not ?" asked Rupert.
To the delight of that criminal investigator, Mr Montmorency's eyes wandered unquietly towards Lieutenant Keith, the only man present that he knew.
"A house-agent," cried Rupert again, bringing out the word as if it were "burglar'.
"Yes...

oh, yes," said the man, with a quavering and almost coquettish smile.

"I am a house-agent...