Anthropologist Lynne Isbell was running through a glade in central Kenya in 1992 when something suddenly caused her to freeze in her tracks. "I stopped just in front of a cobra," she says. "It was raised with its hood spread out."

Isbell, who is at the University of California, Davis, says she has spent the past couple of decades trying to understand how she could have reacted before her conscious brain even had a chance to think — cobra!