A single chemical component of blood creates the pungent metallic scent Count Dracula found so irresistible, research has shown.
In Bram Stoker's original vampire novel, the sharp-toothed Count can hardly contain himself when his guest, Jonathan Harker, cuts himself shaving.
Now scientists know what the undead aristocrat was reacting to - an organic "aldehyde" compound called trans-4,5-epoxy-(E)-2-decenal.
In tests with zoo animals, lumps of wood impregnated with the lab-made chemical triggered a strong response from African and Asian wild dogs, South American bush dogs, and Siberian tigers.
On its own, the compound produced the same reactions - sniffing, licking, biting, pawing and toying - as horse blood.
The carnivores were not bothered with logs coated with fruit essence or a near-odourless solvent.
Tigers were lured most strongly by the blood compound while South American bush dogs lost interest more quickly than other species.
Lead scientist Professor Matthias Laska, from Linkoping University in Sweden, said: "For predators, food scents are particularly attractive, and much of this has to do with blood. We wanted to find out which chemical components create the scent of blood."
Prior to the research, little information existed on the substances that give blood its smell.
Sophisticated chemical analysis techniques eventually identified 30 candidate compounds, any of which could have been what Prof Laska was searching for.
It took the sensitive noses of human scent experts to single out the elusive aldehyde, which they recognised as emitting the distinctive metallic odour typically associated with blood.
The animals tests, conducted at Kolmarden Wildlife Park in Sweden, proved it was this that attracted meat-eating predators.
"How this has developed through evolution is an interesting question," said Prof Laska. "Perhaps there is a common denominator for all mammalian blood."
The research is published in the online journal Public Library of Science ONE.