There was an old lady who swallowed a fly...

I don't know why she swallowed a fly. Perhaps she'll die?
Well, sorry to put a pessimistic and realistic spin of this, but of course she's going to die. Whether it's down to the presence of a fly in her digestive tract being the trigger that sets off all sorts of underlying conditions (such as her stomach lining is sensitive to bluebottles), or that she goes on with her life and dies like a normal person, doing normal things. Like crossing a road or being shanked by an unpleasant individual who coveted her purse. Dying is a fact of life. This lady is seriously not well if she has lived to  be old and still thinks that there is some alternative  method at the end of it all. Or maybe she'll just stay alive for eternity?
Or maybe what the author meant was that perhaps she will die as an immediate consequence of consuming a fly which she doesn't. That makes more sense.

Well, she certainly had enough life in her to consume a spider. In this western world, I don't really see many septuagenarians (or octo- or nonogenarians for that matter) jumping up and down with excitement at the thought of consciously consuming a spider. Especially if it's going to wriggle and tickle inside you, which sounds like a truly unpleasant experience.Of course, everyone eats spiders in their sleep, but that's by accident.
Turns out that this old lady ate a spider in order to catch the fly that was inside her. WHAT DID SHE THINK THAT THE FLY WAS DOING INSIDE HER? BUZZING AROUND? She obviously had no concept whatsoever of what the human internal anatomy resembled. If I remember rightly from the book, she thought there was just a big hole inside her that the fly could buzz around and become a nuisance. Maybe she heard the buzzing ringing in her ears. If you told her that the total surface area of all your internal organs was the size of something large and several football pitches-sized, she wouldn't believe you at all. There couldn't possibly be stuff inside people could there? Of course not, we're hollow.

Little does she know that these poor critters that have unfortunately found their way into her digestive tract, are suffering immense agony and are dead.

Old lady having just swallowed
a horse.

The whole book carries on in this way, with the old lady continuing to eat more ridiculous and equally infeasible organisms in order to "catch" the one that she ate before. This is purely ludicrous. How can a woman swallow an entire horse in one gulp, especially when she has a donkey and a cow and a dog and a cat and probably a couple of other things already in there. Maybe some werthers originals.
I won't spoil the ending, but I must say that it was disappointingly predictable.

I guess that this is a work of fiction, but I hope that the author has reduced his consumption of crack recently. I couldn't think of any other way of coming up with such a bizarre tale.