Zombies probably smell like oleic acid

Excerpts from an interesting column at BBC Earth News:

When animals die, their corpses exude a particular "stench of death" which repels their living relatives... Corpses of animals as distantly related as insects and crustaceans all produce the same stench, caused by a blend of simple fatty acids.

The smell helps living animals avoid others that have succumbed to disease or places where predators lurk. This "death recognition system" likely evolved over 400 million years ago. The discovery was made by a team of researchers based at McMaster University, near Hamilton, Ontario, Canada, and is published in the journal Evolutionary Biology...

The fraction that was so off-putting to other cockroaches contained nothing but simply fatty acids, with oleic and linoleic acids the two main components... They have found that terrestrial woodlice use the same chemistry to recognize their dead, using it to avoid both crushed woodlice and intact corpses. As do two unrelated species of social caterpillar, which usually gather in large numbers...

And because insects and crustaceans diverged more than 400 million years ago, likely from an aquatic ancestor, it is likely that most subsequent species all recognize their dead in a similar way...

"Evolution may have favored recognition of such cues because they are so reliable and exposure to risks of contagion or predation are so important."