scribbling in the margin

I found, as I walked in a yellow wood,
a fork in the road before my feet,
which I stole for the steak and kidney pud
which I held in my hand, for it smelt so good,
I could not forbear to eat.

I shall be telling this with a sigh
somewhere ages and ages hence:
don't wander about with a large meat pie,
and forks in the woods give you E. coli.
Please use your common sense.

I don't know, I've met some pretty affected people in Cambridge

(Mundane answer: there was a mains break near Cambridge, MA, which is not affected because it has a separate water supply. This also explains the first entry. The third should be self-evident.)