Both is right, Elliot: Refusing to give George the plant breaks the quest and missing the speech option with the vampire about him looking familiar - this leads Tutie to admitting why he killed George.
I missed this possibility to break the quest, cause I use all speech options (chatterbox <img src="/ubbthreads/images/graemlins/winkwink.gif" alt="" />)before amusing myself in a fight.
Kiya
