What he says to her is, "Sure." what he was thinking was a little more drawn out, a little more skeptical, sarcasm may have bled in a little, just a tiny bit.
Vampires was not something he knew about. Not Fletcher. To him she might as well of said Fairy. It was the same thing to him. As far as what he actually though? That someone was having a violent time at the expense of these girls and he was planning on putting an end to it with the bulk of his muscle and some fancy shooting if need be.
But the sounds didn't dissipate. They got louder, more violent, sicker. The slurp of something hard and heavy hitting something wet and soft. It wasn't a sexy sound.
Fletcher moved in front of her, gentleman that he was trying to be, and slowly attempted to open the door to peek out silently. The only view the crack in the door afforded him was a sliver of the wall and carpet from the hall so he dared to open the door wider, and eased his head out to have a look at what was happening.
When he saw he pushed her back, closed the door and locked it.
What he saw was a gruesome nightmare - the red would haunt him. There was no other place for that memory to go but to his nightmares.