Do rats really deserve their bad reputation? Are they the hated vermin of yore, or the smartest critters in the food chain? These and other questions provide furtive food for thought on “Rat Genius” (8 p.m., National Geographic).

“Genius” recapitulates some of the astounding and disgusting facts about the large rodents. They can tread water for three days. Their remarkably flexible skeletal structure allows them plenty of wiggle room and the ability to squeeze themselves through almost anything. Most disturbing of all, we are shown, by means of a cut-away piece of familiar family plumbing, that yes, rats can climb up your pipes and surprise you in the toilet.

“Genius” does a grim job of documenting rat infestations in both the posh quarters and rundown sections of Washington, D.C. It also uses night-vision photography to show rats at work around Dumpsters, in kitchens and in walls, jumping from telephone wires and sniffing toasters and coffee percolators. We watch at least half a dozen whiskered rodents hanging out inside somebody’s stove.

“Genius” spends much time in the lab, where rats are outfitted with little hats filled with electric wires. These devices “read” the brain activities of the scuttling creatures and demonstrate how rats learn by replaying the “movie” of past experiences and how these quick-study pantry pests use their remarkable memory to survive and improvise new techniques for foraging and invasion.

What if we could harness rat “Genius” for the good of mankind? The documentary shows just that. Scientists are trying to train rats to sniff out diseases in ailing humans and detect buried landmines in Africa. Betcha those cute meerkats can’t do that!

¢ If the notion of rats treading water in your water closet isn’t terrifying enough, Halloween is just two weeks away. Among tonight’s spectral offerings is the 2006 animated film “Casper’s Scare School” (6 p.m., Cartoon Network), featuring the voices of Jim Belushi and Bob Saget. The cartoon reincarnation of the “friendly ghost” also provides a chance for bicentennial-era pop sensations Captain & Tennille to warble a tune or two. Let’s just hope it’s not “Muskrat Love.”

¢ “NOW” (8 p.m., PBS) looks at the Clean Elections movement, an experiment adopted in Maine and Arizona to help eliminate the influence-buying of big donors and to open the civic process to nontycoons. It profiles Republican Doug Quelland, a two-term conservative who has embraced the “Clean” movement and who is seen campaigning for his third term by walking door to door. “Now” also looks at California as its voters plan to vote on Proposition 89, a law modeled on the Arizona and Maine experiences.

Tonight’s other highlights

¢ A spirit feels out of place on “Ghost Whisperer” (7 p.m., CBS).

¢ On two episodes of “Meerkat Manor” (Animal Planet), Flower gives birth as the desert flowers (7 p.m.), Youssarian baby-sits (7:30 p.m.).

¢ A wealthy wife is murdered at her office on “Close to Home” (8 p.m., CBS).

¢ Jewel guest stars on “Las Vegas” (8 p.m., NBC).

¢ “Dateline” (8 p.m., USA) looks back at the best, or rather the worst, of its “To Catch a Predator” series.