What is the effect of enjambment in this excerpt from "porphyria's lover" by robert browning?

that moment she was mine, mine, fair,
perfectly pure and good: i found
a thing to do, and all her hair
in one long yellow string i wound
three times her little throat around,
and strangled her. no pain felt she;

it creates a sorrowful mood.

it conveys pain.

it enhances the shocking effect.

it introduces a pause.