What does -- mean in a poem?

Question

My Teacher Ate My Homework
My teacher ate my homework,
Which I thought was rather odd.
He sniffed at it and smiled
with an approving sort of nod.

He took a little nibble --
it's unusual, but true --
then had a somewhat larger bite
and gave a thoughtful chew.

I think he must have liked it,
for he really went to town.
He gobbled it with gusto
and he wolfed the whole thing down.

He licked off all his fingers,
gave a burp and said, "You pass."
I guess that's how they grade you
when you're in a cooking class.

-Kenn Nesbitt

Answer 1

In this poem, the dashes work more or less like parentheses. Imagine if the lines looked like this instead:

He took a little nibble
(it's unusual, but true)
then had a somewhat larger bite

The meaning would be the same. "He took a little nibble then had a somewhat larger bite" is really one continuous statement. The other line is an interjection.

Answer 2

just a pause.-- good poem though!! bravo!! did you know that the little dashes on a bomb sight or nasa pictures of the moon are called poems, just a little trivia!!

Answer 3

I would suggest it is a pause for effect.

But you shall have to digest the meanings of "ellipsis" and "lacuna" yourself.