Q:

What is the meaning of this "go in and out"?

What is the meaning of this "go in and out": (from Randall Jarrell’s The Bat-Poet)
The chipmunk said in a pleased voice: "My day." He sat there and listened while the bat said:

  In and out the bushes, up the ivy,
  Into the hole
  By the old oak stump, the chipmunk flashes.
  Up the pole.

  To the feeder full of seeds he dashes,
  Stuffs his cheeks.
  The chickadee and titmouse scold him.
  Down he streaks.

  Red as the leaves the wind blows off the maple,
  Red as a fox,
  Striped like a skunk, the chipmunk whistles
  Past the love seat, past the mailbox,

  Down the path,
  Home to his warm hole stuffed with sweet
  Things to eat.
  Neat and slight and shining, his front feet

  Curled at his breast, he sits there while the sun
  Stripes the red west
  With its last light: the chipmunk
  Dives to his rest.

When he'd finished, the bat asked: "Do you like it?"
For a moment the chipmunk didn't say anything, then he said in a surprised, pleased voice: "Say it again." The bat said it again. When he'd finished, the chipmunk said: "Oh, it's nice. It all goes in and out, doesn't it?"

A:

I think the chipmunk is mostly referring to the rhythm of the poem - the length of each line: long, short, long, short, ..., short, long, short, long.
It certainly looks that way written down: each line alternating in and out. The chipmunk only heard it read however so it would depend on how the bat voiced it but I find myself reading it in an 'in and out' rhythm.
The motion it describes is also quite 'in and out' - the chipmunk moving hither and thither. That's especially true, of course, of the first three words.
The two combined makes it an apt and poetic description of the poem to me.

