It's only the use, the result of using the key that is sent back and forth.

"How much sending back and forth will there have to be first?"

And this is what the dark mud can send forth.

E-mail messages were sent back and forth, though I haven't read them.

At first it must have seemed to those who sent forth the picture of a dead man that their tactic was working.

And so the word went out among the elders: Send forth a leader.

Their teenagers are sent back and forth between them so as to spend time with each parent.

In 1812 it sent forth its first missionaries to India.

She is the bow from which I, a living arrow, am sent forth.

When it finds one, connection details are sent back and forth.