There are several motifs throughout the book: one is blood. In his rage, Robert is prone to inflicting cuts and scrapes on himself, and at other times, he is scratched and clawed by vampires. Robert draws blood on these occasions, which are thematically linked to his investigations of the vampires' circulatory systems. The term "blood" is also used from time to time to refer to Robert's father Fritz, from whom he has inherited his scientific temperament.