Some people claim immunity from tickling, and no one seems to be able to tickle themselves. The ribs, underarms and feet are the most effective tickle targets. Dr. Curt Stager and Martha Foley continue their discussion with the anatomy of tickling.

Some people claim immunity from tickling, and no one seems to be able to tickle themselves. The ribs, underarms and feet are the most effective tickle targets. Dr. Curt Stager and Martha Foley continue their discussion with the anatomy of tickling.

Why are humans ticklish? Does it have a purpose? How you react to tickling depends on who is doing the tickling.

Why are humans ticklish? Does it have a purpose? How you react to tickling depends on who is doing the tickling.

Why are humans ticklish? Does it have a purpose? How you react to tickling depends on who is doing the tickling.

Gene sculpting has gained cautious acceptance for medical research and treatment, but a bioluminescent rabbit created by a "transgenic artist" for aesthetic purposes pushes the limits of the debate.

Gene sculpting has gained cautious acceptance for medical research and treatment, but a bioluminescent rabbit created by a "transgenic artist" for aesthetic purposes pushes the limits of the debate.

As the secrets of the natural world give way to science, it's nice to know some mystery remains. Dr. Curt Stager and Martha Foley explore one of the last great conundrums: How do cats purr? Science has theories, but no definitive answer.

As the secrets of the natural world give way to science, it's nice to know some mystery remains. Dr. Curt Stager and Martha Foley explore one of the last great conundrums: How do cats purr? Science has theories, but no definitive answer.

Dr. Curt Stager and Martha Foley revisit this feisty predator, whose fierce reputation comes from a high metabolism and the need to consume 80-90 percent of their body weight in food each day to survive. The small insectivore is active throughout the winter and shrinks in size until spring.