A new view of leeches; SETI — the search for extraterrestrial intelligence; stem cells; and a profile of Edie Widder, a specialist in marine bioluminescence.

"Leeches"--Leeches, those innocent bloodsuckers, have been bad-mouthed to the point that they've become synonymous with obnoxious freeloaders. Even host Neil deGrasse Tyson is creeped out while wading through leech-infested waters with scientist Mark Siddall, who runs the leech lab at the American Museum of Natural History. Siddall notes that leeches are far less dangerous than mosquitoes and ticks as disease spreaders. They've recently made something of a comeback, and are today used when reattached fingers and toes become engorged with excess blood that must be drained off. Leeches are hermaphrodites and exist in countless species and ecological niches throughout nature. You'll gain new respect for these fascinating little creatures and never use their name in vain again.

"SETI"--In 1960, a curious astronomer named Frank Drake aimed a radio telescope at a couple of nearby stars and started listening. More than 40 years later, we're still listening, and SETI - the search for extraterrestrial intelligence - has just expanded big-time to begin the systematic survey of millions of star systems for signs of advanced civilizations. NOVA scienceNOW reports on this impressive new effort, called the Allen Telescope Array. The project is underwritten primarily by billionaire philanthropist Paul G. Allen and will eventually comprise 350 giant dish antennas, all working in unison to answer the question: Are we alone?

"Stem Cells"--Researchers around the world are touting a possible new way of creating embryonic-like stem cells - without the embryo. Japanese researchers were the first to discover a way to "turn back the clock" on adult skin cells to create what look like embryonic stem cells - special cells normally found in a growing embryo that have the ability to become any type of cell in the body. Building on the Japanese discovery, U.S. researchers have since been creating these stem cells from human skin cells, with the hopes of possibly using these cells to understand diseases like diabetes, Alzheimer's and Parkinson's. Though the new method offers a potential alternative to the ethically charged work of using human embryos to isolate these important stem cells, the technique still has a number of obstacles to overcome and has scientists warning this is certainly not the end of the debate.

"Edith Widder"--Go for a deep-sea dive with a scientist who is seeing things never before recorded on the ocean floor. Edie Widder is a specialist in marine bioluminescence, the biochemical emission of light by ocean animals that can light up the murky depths to an astonishing degree. Widder is doing some lighting of her own with an innovative camera system called the "Eye in the Sea," which uses a wavelength of light invisible to sea creatures. On its first test, the "Eye" recorded a squid unknown to science. Widder's research has won her a MacArthur "Genius Grant," which will help support her work at the Ocean Research and Conservation Association, of which she is a co-founder.