About this scene
She comes around the corner of the periodicals section looking for a reference book. He's standing there with the BBC already out. She does not say anything. She does not ask. She drops her bag on the carpet and goes down to her knees within four seconds of seeing him. The whole encounter is silent except for the sounds you'd expect, and a phone ringtone three rows over near the front desk. She finishes him in her mouth and stands up to leave without making eye contact.
What to watch for
The silence is the discipline. Most amateurs talk through the buildup. She doesn't say a word. Her movements are economical and she sets a steady rhythm without looking up to check his face. The ringtone in the background is real ambient audio. It rings four times, goes to voicemail, and you can hear the front desk pick up the receiver. None of that breaks her focus.