Koalas look like the sweetest, cutest, gentlest creatures on Earth.
"You might think that a koala's life is quiet and peaceful," said Fred Kaufman, the executive producer of Nature (7 p.m., PBS/Ch. 7) "But in reality, their life is full of struggles, vicious fights, even deception - at least while they are awake. They sleep up to 18 hours a day, and they spend almost the rest of their free time eating eucalyptus leaves, a diet poisonous to most mammals."
The documentary "Cracking the Koala Code" is about attempts to understand the sounds the animals make. Is it a language?
But it also shows us koala society, where the male dominates.
"Because he's the boss, he gets to mate with all of the females in his territory," Kaufman said. "During mating season, he shows many aggressive territorial and courting displays that goes against a koala's often assumed sweet nature.
"It's kind of the "Desperate Housewives,'" said filmmaker Tina Dalton. "There's cheating going on. There's fighting. There's sneaking around people's backs."
In other words, don't let your little kids tune in to watch "Cracking the Koala Code."
Elsewhere on TV ...
The Middle (7 p.m., ABC/Ch. 4): Frankie pumps Brick for information about Axl and Sue.
Betty White's Off Their Rockers (7 and 7:30 p.m., NBC/Ch. 5): Back-to-back episodes of this senior citizens' version of "Candid Camera."
American Idol (7 p.m., Fox/Ch. 13): The three remaining contestants perform.
Suburgatory (7:30 p.m., ABC/Ch. 4): Tessa feels left out when Chatswin celebrates mothers. (Season finale)
Criminal Minds (8 and 9 p.m., CBS/Ch. 2): The team negotiates a hostage crisis; Prentiss says goodbye. (Season finale)
Modern Family (8 p.m., ABC/Ch. 4): Claire and Cameron disagree over child-rearing.
Don't Trust the B--- in Apartment 23 (8:30 p.m., ABC/Ch. 4): An embarrassing video of James and Chloe is leaked.
Revenge (9 p.m., ABC/Ch. 4): A devastating loss brings Jack and Emily closer.
Law & Order: Special Victims Unit (9 p.m., NBC/Ch. 5): While searching for a missing teen, the detectives find a severed leg.
Hot In Cleveland (11 p.m., TV Land): The women bid on the contents of an abandoned storage unit,
Happily Divorced (11:30 p.m., TV Land): Fran dates a doctor.