Scrappy-Doo is in this movie, too. He urinates on Daphne. In another scene, Scooby and Shaggy have a belching contest that regresses into a flatulence contest.

Now, why were you thinking of watching this? Nostalgia, was it? Or were you hoping the film would mock the TV series, the way the “Charlie’s Angels” movie did? In either case, you lose. The film imitates many ideas from the cartoon without capturing any of the spirit, and it is only occasionally self-aware enough to kid itself.

I frankly don’t know what the concept was here, except to appeal to little children. It does that, I’m sure, with lowbrow humor, simple jokes and a plot so convoluted that only kids could forgive its not making sense.

It begins with the Scooby gang breaking up for nebulous reasons. Nerdy Velma (Linda Cardellini) is upset because Fred (Freddie Prinze Jr.) always takes credit for her ideas that help catch the bad guys; beyond that, there is not much apparent reason for the split. Fred goes on the lecture circuit, Daphne (Sarah Michelle Gellar) takes up martial arts, Velma does nerdy science stuff, and Shaggy (Matthew Lillard) and Scooby (voice of Scott Innes) head to the beach to be slackers.

They are all reunited within five movie minutes, each amateur sleuth having been separately invited to pursue a mystery at an amusement park called Spooky Island. The owner, Mondavarious (Rowan Atkinson), is worried because teens are leaving the island as mindless zombies, something apparently having influenced them during their stay.

Producing a live-action version of a cartoon puts it into reality, which forces you to ask questions that can go ignored when you’re watching animation. Why do Scooby and Shaggy get so excited about Scooby Snacks, for example, when they can apparently be purchased at any grocery store? And why are they called Scooby Snacks? Was the dog named after the snack, or did Scooby’s ghost-catching exploits become so famous that they named a snack after him? (In that case, he should have a free lifetime supply anyway.)

And you’d think they would stop being scared of ghosts after a while, considering they turn out to be imposters 100 percent of the time.

And let’s not forget something else: Scooby-Doo is a TALKING DOG.

Not to be a spoil-sport, but if you’re going to make a movie in which everyone talks and acts like cartoon characters, why not just make a cartoon? Movies like this have a strong smell of “stunt” about them, like someone thought it would be funny to find real-life actors who look like beloved cartoon figures, and then didn’t think much beyond that point.

As much as I have never enjoyed a Matthew Lillard performance in anything, I have to admit he’s a good Shaggy. He captures the voice and the body movements perfectly, and you’d never know most of his acting was opposite empty air (Scooby having been inserted later, of course). Linda Cardellini is also somewhat interesting as Velma, and Rowan Atkinson is amusing in virtually anything.

Meanwhile, as much as I love Sarah Michelle Gellar as Buffy (you know, the vampire slayer), she’s pretty bland as Daphne. Ditto her boyfriend, Mr. Prinze Jr., who is, surprise surprise, a waste of space as Fred.

This movie is not for people who grew up watching “Scooby-Doo” cartoons in the ’70s and ’80s. It will not entertain them, unless they are still the same age they were then. If this movie is for anybody — and that is open for debate — it is for young children. Their parents would do well to cram earplugs in their ears and put pillowcases over their heads for 87 minutes.

D+ (1 hr., 27 min.; PG, one mild profanity, some crude humor, comic violence.)