Question

What would most likely cause the wolf to lie down belly up?

Answer 1

Most likely a wolf would lie down belly up to
show submission

This is a friendly amd submissive gesture because when its doing this its trying to look smaller

It'll also roll over to show a dominant wolf that
it is helpless and not aggressive

Answer 2

In submission to an alpha wolf, another wolf shows his or her belly. The alpha wolf then has the choice to kill, to accept or to run the wolf