Have you heard the concept, in television, of a show "jumping the shark"? A show jumps the shark when it reaches its peak and you know it will all be downhill from there. The expression derives from an episode of Happy Days in which the Fonz was on waterskis and jumped over a shark, or something like that. I never watched that show, but that's the explanation on the Website, www.jumptheshark.com How do you know when a show has jumped the shark? You feel it, of course, but there are a few surefire signs: a character is suddenly played by a new actor; a baby is born; characters who always hated each other get married; a once-realistic show suddenly features kidnappings and evil twins. A great example of a show jumping the shark is Melrose Place. After a rocky start, it became an enjoyable guilty pleasure, but then it degenerated into a series of crazy plot turns that made no sense and were not even enjoyably over-the-top. Melrose Place is showing at a 12:45 a.m. most nights on YES Stars 3 and HOT 3, but I can tell the other insomniacs out there that by the time you read this, the shark will have been jumped. The reruns are just about at the end of Season Three, when a crazed Dr. Kimberly Shaw (Marcia Cross, who now plays Bree on Desperate Housewives) blows up the entire apartment complex, killing a few minor characters and maiming a couple of stars. After that, Kimberly becomes a radio psychiatrist while she's in a mental institution, then kidnaps Dr. Peter Burns and hides him a locked ward, and then - who cares? You get the point though, when it's not fun anymore, it's jumped. (And before anyone turns his or her nose up at me for admitting I was a Melrose Place fan, let me remind you of the Seinfeld storyline in which his policewoman girlfriend gives him a polygraph test to see whether he was telling the truth when he claimed never to have watched Melrose. Of course, Jerry fails the test.) So how does the jump-the-shark concept relate to today's shows? Just about every night, you can catch two of the series in the "Never Jumped" Hall of Fame (a show gets this honor when it receives a certain number of votes on the Website): The Simpsons, which airs on Channel One at midnight on weeknights, and The Sopranos, which is on Yes Stars 2 weeknights at 11:10 p.m. The often exciting and intricately plotted Heroes, which just finished its first season here, definitely has not jumped yet, but it's an open question how long it can sustain its suspense and inventiveness during its new season. My two candidates for new shows that will join the "Never Jumped" Hall of Fame are Weeds and Big Love, both of which air on YES. The first two seasons of Weeds have already been broadcast and the third season, which has just begun airing in the US, will be back in a few months. The second season of this show about Nancy, the pot-dealing suburban mom (Mary-Louise Parker), hovered dangerously close to jumping, especially with all the plot complications regarding her relationship with Peter (Martin Donovan), a DEA agent with whom she gets romantically involved before she knows what he does for a living. Most of the show, though, was up to or almost up to the first season's almost impossibly high standards for wit, drama, superb acting and the occasional twist. Here in Israel, we've only seen the first season of Big Love, the story of an upscale polygamous family, an off-shoot of the Mormons. It was wonderful, and anyone who saw it is looking forward to the second season, which will air in the fall. Although it might sound as if these shows are about people you wouldn't want to know, the truth is that, like The Sopranos they are simply shows about complicated and often dysfunctional families. The pot-dealing and polygamy are just devices for exploring the characters. So check them out when they air and then go to JumptheShark.com and rate them yourself.