Mystery short story where the owner of a dog is accidentally murdered via strychnine

Question

I solved this one in the process of asking the question, so I'm self-answering.

I remember it as being part of an Alfred Hitchcock anthology. The protagonists get pulled into investigating the murder of an old lady who's found dead on her kitchen floor (I remember very vividly the black-and-white drawing of her contorted body lying there) with no apparent motive for murdering her. It is found that the hamburger that she ate that night was poisoned with strychnine. Eventually, the protagonists determine that the actual intended victim was her dog, who she had written into her will. The killer had seen that she had bought steak and hamburger, and poisoned the hamburger, assuming that would be the dog's food, but she'd given her dog the steak and eaten the hamburger.

It may have appeared in the same anthology as "Yours Truly, Jack the Ripper" by Robert Bloch.

Answer 1

"Puzzle for Poppy" by Patrick Quentin

Looking up "Yours Truly, Jack the Ripper" led me to the ISFDB page, which listed two Hitchcock anthologies that included the story, Alfred Hitchcock's Fireside Book of Suspense and Alfred Hitchcock's Spellbinders in Suspense, the latter of which looked very familiar, but none of the listed entries matched up. However, in a search on one of the titles, I came upon the Goodreads entry for the book, which listed more stories. Of course, this one would not be science fiction or fantasy, and therefore would not be on ISFDB. A bit more searching, and I found that it was "Puzzle for Poppy". This review mentions some salient details:

What do Peter and Iris Duluth, a last will bequest, a nervous guardian, and a pregnant St. Bernard have in common? It will take a realization on Iris’s part (one very reminiscent of a well-known G. K. Chesterton story) and a lucky shot by a precocious little girl with a charming lisp to expose (and we do mean “expose”) a carefully-planned murder plot against an unusual intended victim.

The excerpt of her seeming death (it turns out that she survived the experience):

Poppy was crouching on the carpet, her huge muzzle dropped on her paws. She was howling and staring straight at Miss Crump.

Poppy’s paid companion was on the floor too. She lay motionless on her back, her legs twisted under her, her small, gray face distorted, her lips stretched in a dreadful smile.

I believe this is the illustration I remember, apparently by Harold Isen.

In addition, I was wrong that Mrs. Crump was dead. She had to stay in the hospital to recover for a time, leading to Iris and Duluth getting to make a bit of money dogsitting for her until her return.