What to shout?

i generally find that if i shout no in as deep and authoritive a tone as possible they freeze.
in their mind they are weighing up if their dash for the other side of the road will be smooth or rough. a booming no! tends to answer the question. one day i might try "freeze!"

+1 to that.

"Waaaake UP!" also works. I think of it as snapping them out of a hypnotic state, which is the only explanation for Cornhill/Poultry/Cheapside peds I can think of.