I usually have catch factor=0, and I use route to find the next airwire,
but when there is none left, clicking does noting, as if your mouse
button is broken.
It would be nice to get a response in the status bar, like "no airwires
found [, but some are hidden by ratsnest]".
If catch factor is set or some are hidden, more information can be
displayed, like suggested in square brackets.