He was, in this aspect, but a higher and more intelligent rendering of the trees around her.

In another aspect he was an opportune victim, something to strike at.

When the anger of a poison snake opens its gland, and the fang is charged with venom, it must strike at something.

It does not pause or consider what it may be; it strikes, though it may be at stone or iron.

So Stephen waited till her victim was within distance to strike.