In the title of this blog post, the old lady is hypothetical, the young man is real, and so is the shrew.
The old lady appears in this item in the Cardunculus blog:
One of the cats was sick in the gravel, but the Systems Administrator had to clear it up as I was out at the time. The sick apparently contained what initially appeared to be an enormous fur-ball, but turned out to be an entire shrew, swallowed whole. On being told of this event I composed a short verse:
There was an old lady who swallowed a shrew
What an odd thing to do
To swallow a shrew
Perhaps she’ll spew
It was that sort of day really.
The young man, quite real, appears in the research study honored by the 2013 Ig Nobel Prize for archaeology. That prize was awarded to Brian Crandall and Peter Stahl, for parboiling a dead shrew, and then swallowing the shrew without chewing, and then carefully examining everything excreted during subsequent days — all so they could see which bones would dissolve inside the human digestive system, and which bones would not.
The study is: “Human Digestive Effects on a Micromammalian Skeleton,” Peter W. Stahl and Brian D. Crandall, Journal of Archaeological Science, vol. 22, November 1995, pp. 789–97.