In Chapter 8 of 1984, what is Winston's first reaction when he sees the dark-haired girl on the street and what action does he consider?

In Chapter 8, Winston sees the dark haired girl (who is, of course, Julia) on the street.

His first reaction to her is real fear.  He is sure that she has been sent to spy on him by the thought police.  He imagines that her presence is proof that they are "on to" him.

When he sees her what he does is to consider killing her.  He wonders if the piece of glass he is carrying will be heavy enough to do the job.  In the end, of course, he figures that he wouldn't be strong enough to kill her easily, so he doesn't try.