Spike has been attempting to bite Angel, though he forgot to go into gameface, which doesn't help anything at all. When Buffy says that he looks up in horror and immediately rolls off from on top of Angel and stumbles away from him.

"No! We didn't!" He glares at Angel. "Now look what you've done. First you told Cordelia, now her? Why not just scream it out where everyone can hear it?" Because apparently he's not even going to pretend his denial was convincing.