It ain't profitsome, fellers, to ruminate
'bout the final grub Harry S. Truman ate.
I say slice up his rumen
And check it! Assumin'
We get the OK to exhuminate.


Stuff some offal inside of a rumen,
Add spices – like nutmeg or cumin –
And oats. There's your haggis,
Now eat it! (To gag is
To prove that your own stomach's human).


Based on the suggestion: “rumen”

I don't really dislike haggis all that much (nor do I believe in the profitsomeness of discovering what HST's last meal was).  I just go where the rhymes lead me.