“The Final Member” screens at 10 p.m. Saturday at the Union South Marquee.

Everybody needs a hobby. For Siggi Hjartarson, it was collecting penises.

It started with a dried bull penis, and then grew to a private collection, and then finally a museum in Iceland devoted to displaying the equipment of every species of animal on Earth. (It’s like Noah’s Ark, although Siggi only lets in one of each.) Except one.

Man.

The hilariously straight-faced documentary “The Final Member” chronicles Siggi’s quest to find that lucky donor. Like any good Christopher Guest mockumentary, it’s full of oddball characters who take something way more seriously than they should, and it pulls up just shy of openly making fun of them.

Siggi, in particular, cuts a rather sympathetic figure, an old man who tends to his cows, loves his family, and is a scholar on the side who translates centuries-old books. He just wants a legacy to live on after he goes, and a museum full of penises dunked in formaldehyde has somehow become that legacy.

At first, Siggi has a donor — 93-year-old “adventurer” Pall Arason, who claims to have slept with hundreds of women, which makes you wonder when he made time for “adventuring.” But Pall is getting up there, and Siggi worries that certain aging processes (in the words of George Costanza, “shrinkage”) will mean the specimen isn’t big enough for his museum.

Enter an American, Tom Mitchell, and “Elmo.”

Elmo is certainly big enough to make it into the museum, but Tom is one seriously weird dude. He’s obsessed with his little sidekick (frontkick?), dressing him up in little costumes, getting him a stars-and-stripes tattoo, even commissioning a comic book starring Elmo. Tom is so thrilled at the idea of Elmo becoming famous that he’s even considering donating Elmo to the museum WHILE HE IS STILL ALIVE to head Pall off at the pass. If Tom wasn’t a real person, Will Ferrell would have had to invent him.

Much hilarity ensues, including a riotous sequence in which Pall tries to get a plaster-of-Paris cast of his equipment made, with disastrous results. Ouch. In the end, Siggi gets his museum acquisition, and the rest of us have watched a very strange and funny film. (By the way, one of the editors of the film is a UW grad, whose name is . . . and I’m not kidding . . . Andrew Dickler.)