Dumb Witness is a detective fiction novel by British writer Agatha Christie, first published in the UK by the Collins Crime Club on 5 July 1937[1] and in the US by Dodd, Mead and Company later in the same year under the title of Poirot Loses a Client.

The author does "this sort of thing so superlatively well",[5] while The Times in London questioned one of the actions by the murderer: "who would use hammer and nails and varnish in the middle of the night near an open bedroom door?

[11] Wealthy spinster Emily Arundell writes to Hercule Poirot in the belief she has been the victim of an attempted murder after a fall in her Berkshire home.

After Poirot receives the letter, he travels to Miss Arundell’s home, only to learn she is dead; her physician, Dr Grainger, states her death was from chronic liver problems.

Seeking to investigate Miss Arundell's belief that someone wanted to murder her, Poirot, accompanied by Captain Hastings, notes that under her previous will, her nephew Charles and nieces Theresa and Bella would have inherited.

Visiting the house on the pretence of buying it, Poirot discovers a nail covered with varnish at the top of the stairs and deduces a string had been tied to it.

During his investigation, Poirot learns that a luminous aura was noticed coming from the dead woman's mouth when she spoke during a seance.

At the same time, Miss Lawson's gardener recalls Charles inquiring about his arsenic-based weed killer and is surprised to find the bottle containing it nearly empty.

When the attempt with the tripwire failed, she filled one of Miss Arundell's patent capsules with elemental phosphorus, knowing the poison would mimic the symptoms of liver failure.

Poirot reveals that Miss Lawson saw Bella on the night of Emily's fall, though in a mirror; the brooch's initials were reversed from that of "AT" – Arabella Tanios.

Knowing Emily wished for no scandal, Poirot honours this, while Miss Lawson decides to share her inheritance with Theresa, Charles, and Bella's children.

John Davy Hayward in the Times Literary Supplement (10 July 1937), while approving of Christie's work, commented on some length at what he felt was a central weakness of this book: "Who, in their senses, one feels, would use hammer and nails and varnish in the middle of the night within a few feet of an open door!

"[6] In The New York Times Book Review (26 September 1937), Kay Irvin wrote that "Agatha Christie can be depended upon to tell a good tale.

She is not doing her most brilliant work in Poirot Loses A Client, but she has produced a much-better-than-average thriller nevertheless, and her plot has novelty, as it has sound mechanism, intriguing character types, and ingenuity.

Apart from a certain baldness of plot and crudeness of characterisation on which this author seemed to have outgrown years ago, and apart from the fact that her quite pleasing dog has no testimony to give either way concerning the real as opposed to the attempted murder, her latest book betrays two main defects.

But the detection is good, and the reader has no ground for complaint, for the real clue is dangled before his eyes several times, and because it seems a normal feature of another phenomenon than poisoning that he tends to ignore it.

"[10] E. R. Punshon of The Guardian began his review column of 13 July 1937 by an overview comparison of the books in question that week (in addition to Dumb Witness, I'll be Judge, I'll be Jury by Milward Kennedy, Hamlet, Revenge!

by Michael Innes, Dancers in Mourning by Margery Allingham and Careless Corpse by C. Daly King) when he said, "Only Mrs Christie keeps closer to the old tradition, and this time she adds much doggy lore and a terrier so fascinating that even Poirot himself is nearly driven from the centre of the stage."

"[5] In the Daily Mirror (8 July 1937), Mary Dell wrote: "Once I had started reading, I did not have to rely on Bob or his cleverness to keep me interested.

However, in the audiobook edition read by Hugh Fraser, the boy is always called Edward, even in those two instances where the print version has the wrong name.

[13] "The Incident of the Dog's Ball" was published in Britain in September 2009 in John Curran's Agatha Christie's Secret Notebooks: Fifty Years of Mysteries in the Making.

BBC Radio 4 broadcast a full cast adaptation of the novel in 2006, featuring John Moffatt as Hercule Poirot and Simon Williams as Captain Arthur Hastings.