In season 2 Xander says:
about Angel
then in season 6 buffy says:
to Spike
I get why it was said to Angel, but shouldn't Buffy have been able to sense Spike behind her?
XANDER: That's it, I'm puttin' a collar with a little bell on that guy.
about Angel
then in season 6 buffy says:
BUFFY: Bell. Neck. Look into it.
to Spike
I get why it was said to Angel, but shouldn't Buffy have been able to sense Spike behind her?