Despite leaving his office open out of habit - an odd habit to have around Fabletown, but he does it to seem more friendly - he hadn't anticipated anyone actually coming in. So being spoken to spooks him, and it takes him a moment to turn and face him.

"Everything's fine, I'm just..." he waves a cigarette lazily as he tries to figure out an excuse, "...Thinking on my feet. Works better in here where I can't disturb anyone."

Yeah, good one, Bigby.