I KNOW what the caged bird feels, alas!
When the sun is bright on the upland slopes;
When the wind stirs soft through the springing grass,
And the river flows like a stream of glass;
When the first bird sings and the first bud opes,
And the faint perfume from its chalice steals —
I know what the caged bird feels!
I know why the caged bird beats his wing
Till its blood is red on the cruel bars;
For he must fly back to his perch and cling
When he fain would be on the bough a-swing;
And a pain still throbs in the old, old scars
And they pulse again with a keener sting —
I know why he beats his wing!
I know why the caged bird sings, ah me,
When his wing is bruised and his bosom sore,—
The dash at the end of this line serves as a voluntary return to the irregular, inverted rhythm. 
 Again, the rhythmic delineation of the lines reflects their content: At the end of the second stanza, the pathetic fantasy is over, but not because it’s unsustainable within the cage: The bird beats its wing to renew and refresh its pain, to ward of complacency and confront its reality.
Sympathy