Considering his general silence in the tank up until the point the bubbles happen, it's only natural that the sound catches Sybil's attention. She glances slightly from her seat and then slowly rises.

At the edge of the tank, she places a hand against the glass and taps just once with a metal-tipped fingernail. She knows how to make a small sound in the water, she doesn't want to hurt him with the sound after all he's been through.

But she knows talking isn't the ideal way to get his attention right now.