Walter's still dwelling on what, if anything, he should do or say, when the ghost woman is straightening up and leaning towards him.

Then she kisses him. He freezes in place, eyes wide, brain not quite catching up to what's happening until it's very much happening. She's kissing him. People don't kiss him; people don't even touch him. He can't even manage a real reaction to it. He just... goes blank. Shuts down completely. Even breathing requires too much brainpower, and he is very much incapable of any, at the moment.