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When they both worked at Princeton, Howard Stone and Jeff Aristoff used to play basketball at lunchtime. One day, when Dr. Stone was warming up with his jump rope, the two wondered if anyone had mathematically modeled the shape of the rope. The two researchers decided to give it a whirl.

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JOE PALCA, HOST:

This is SCIENCE FRIDAY. I'm Joe Palca. Ira Flatow is away this week. The biotech company AquaBounty Technologies of Waltham, Massachusetts, has developed a genetically modified Atlantic salmon that grows twice as fast as regular salmon. How has it done this? By tinkering with the salmon's genome, adding a growth hormone gene from one fish plus an antifreeze gene from another.

Adult Burmese pythons can swallow prey as large as deer. Now, researchers from the University of Colorado, Boulder say the way the python's heart balloons after it eats could help treat human heart disease. Molecular biologist Leslie Leinwand discusses her team's python experiments.

Reporting in Science, researchers write of an experiment in which rats worked to open the cages of trapped rats, but not empty or dummy-filled cages. Author Peggy Mason discusses empathy in non-primates, and the value rats place on freeing a companion--about equal to that of a stash of chocolate chips.

In Asia's Space Race: National Motivations, Regional Rivalries, and International Risks, Naval Postgraduate School professor James Clay Moltz discusses the potential militarization of fast-growing space programs in China, India, and Japan--and why US military officials are keeping watch.

Presenting at a meeting of the American Society of Tropical Medicine and Hygiene, researchers said bedbugs can survive many generations of inbreeding, allowing one pregnant female to cause a building-wide infestation. Biologist Rajeev Vaidyanathan discusses that study, and another on pesticide resistance.

The news that Rep. Michele Bachmann (R-Minn.) and Gov. Rick Perry (R-Texas) have decided not to participate in the Dec. 27 Republican presidential debate that businessman/TV personality/self-proclaimed potential independent presidential candidate Donald Trump is supposed to be moderating means just two GOP contenders would be left for the event:

Former House Speaker Newt Gingrich (Ga.) and former Sen. Rick Santorum (Pa.).

On Saturday, college football's best player will be awarded the Heisman Trophy in New York. This year's front-runners attend Baylor University, Stanford University and University of Alabama; but 75 years ago, the Heisman winner was a Yale man. In 1936, at a time when the Ivy League was a hotbed of football talent, Yale end Larry Kelley was the first to win a Heisman Trophy.

The U.S. trade deficit narrowed in October to its lowest point of the year as Americans bought fewer foreign cars and imported less oil. Exports of American-made autos also fell.

Virginia State Police and other officials briefed reporters this morning about Thursday's shooting on the campus at Virginia Tech, in which a campus police officer was killed and the suspect apparently later shot himself and died. We updated as it happened and put those posts in chronological order after the briefing was over.