The path that Vincent walked down, seemed to be rather quiet, that is, until in the distance, he heard a voice, the voice belonging to a Little Sister, a smirk appearing across his face as he then heard the loud groan of a Big Daddy "Finally, some more ADAM...." he chuckled lightly to himself.
He put his shotgun onto his back and grabbed his rocket launcher instead, putting a rocket into it as the Big Daddy slowly walked into view "Let's do this big guy..." he chuckled some more as he aimed his rocket launcher at the Big Daddy before firing, damaging the Big Daddy and catching its attention as well, to which it charged at Vincent.
Vincent stood there, a smirk still upon his face and once the Big Daddy was in range, he froze it on the spot before using his lightning upon it, weakening it even further before pulling out a grenade, pulling the pin and tossing it down underneath the Big Daddy, stepping back in time as it exploded, causing the Big Daddy to fall down.
The Little Sister in question, rushed over to her guardian and started to sob "Mr. Bubbles! Please get up!" and that's when Vincent grabbed her by the throat, harvesting her instead of rescuing her, getting as much ADAM as he could from her, the slug being destroyed before searching the Big Daddy for whatever he had on him at the time.
There was nothing as Vincent went back to what he was doing earlier on, finding out the source of the voices from earlier on "Come out, come out, wherever you maybe"