Walter's own expression changes on a dime as he notices the shift in Ben's posture.

That he recovers enough to send the plane is reassuring, and Walter reads the note before coming over, but he still elects to answer him from right nearby.

He also still writes out his reply, more for Ben's sake than anything, rather than speaking aloud.

That does indeed sound useful, but are you alright?

The 'you' was underlined for emphasis.

There may be something suitable by the cliffs.

Not that Walter knows what's under there just yet.