Are we to interpret this as Jason actually intending to continue from there (in a Mother’s Day card)? I’m not sure how you can know that opening without knowing it doesn’t end well.
Unless, I guess, this was all perfectly innocent and Andy actually comes from Nantucket. Which some people must, after all.
Comics I Don't Understand 
I think we’re supposed to assume that Jason doesn’t know how it goes on from there. He thinks it’s a standard poem opening along the lines of “Roses are red, violets are blue”.He’s only 10, after all, and virtually all of his precociousness is in STEM subjects.
Limericks (even clean ones) hardly qualify as “romantic” poetry, and those that mention “Nantucket” in the first line tend to have a word in the last line that rhymes with “…uck“.
There once was a mom from Nantucket
Who put up with all sorts of ruckus
I for one
Am glad she had sons
And didn’t decide to chuck it.
Yes, but Jason may not know that.
There once was a man from Nantucket
Who kept all his cash in a bucket.
His daughter, named Nan,
Ran off with a man.
And as for the bucket, Nantucket.
I expect that if Jason did come up with a limerick that started that way, it would end with an equation.
There once was a lass from Nantucket
Who washed out her things in a bucket
Till the winds and the breezes
Blew away her chemises
So she threw up her hands and said, “to heck with it.”
I want to know what’s happening to Jason’s head in the first panel. Are his eyebrows turning into a flock of birds? Why is he sticking his tongue out?
He is raising his eyebrows up and down.
There once was a man from Nantucket
who carried wet glue in a bucket.
‘Till once did he trip
and lose his firm grip.
Then putting his foot down, he stuck it.
Perhaps he is a follower of Edward Lear, whose limericks usually (and rather lamely) ended with the exact same word as the word used at the end of the first line.
http://ingeb.org/songs/edwardle.html for some egg samples.
Da Yadda da yadda nantucket
Ya Dada ya dadada bucket
Then two random lines
The ends of which rhymes
And then anything else but the words, “fuck it”
See, I actually knew the clean versions of the “Nantucket Limerick” before I even knew there were dirty versions.
That first one that Susan T-O posted, and then the sequel verses:
There once was a man from Nantucket
Who kept all his cash in a bucket.
His daughter, named Nan,
Ran off with a man.
And as for the bucket, Nantucket.
Pa followed them all to Pawtucket —
The man, the girl Nan, and the bucket —
Pa said to the man
He was welcome to Nan
But as for the cash, well, Pawtucket.
But the pair followed Pa to Manhasset
Still carrying the cash as an asset
Nan and the man
Stole the money and ran,
And as for the bucket, Manhasset.
I never knew about the “bucket of cash” number before this thread. I had made mine up just to annoy people who expected a dirty limerick from the first line. I guess the coincidence of the rhyme “bucket” must stem from the limited number of options.
From W. S. Gilbert:
There was an Old Man of St. Bees
Who was stung in the arm by a wasp.
When asked, “Does it hurt?”
He replied, “No, it doesn’t,
But I thought all the while ’twas a hornet.”
There once was a man from Peru
Whose limerick stopped at line two.
There once was a man from Iran
Whose limericks never would scan.
When he was asked why
He gave this reply,
“I just can’t help putting as many syllables in the last line as I possibly can.”