As the closing credits rolled for "Other People" during its premiere at the Sundance Film Festival, a familiar sound reverberated around the theater: the barely audible sniffles of people futilely trying to conceal their crying. Interestingly, the woman to trigger so much weeping was Molly Shannon, the same comedian who made us laugh while kicking, stretching and kicking as Sally O'Malley, the same gangly SNL alum who channeled "superstar" Catholic schoolgirl Mary Katherine Gallagher.

Sundance seems to be the place to debut such a transformation. This is the festival where Kristen Wiig and Bill Hader first demonstrated their Serious Thespian Skills in the family drama "The Skeleton Twins." And last year, Sarah Silverman showed off some major acting chops playing an addict and mother of two in "I Smile Back." Sundance is also where Steve Carell proved he was more than a sitcom guy when he took on the role of a depressed academic in "Little Miss Sunshine."

In the case of "Other People," Shannon isn't entirely to  blame (or celebrate) for the blubbering. The movie used the old cancer trick, which is a pretty surefire way to guarantee waterworks. Nevertheless, Shannon's moving performance made the movie even more profoundly tragic. The actress plays Joanne, the mother of three kids ranging in age from 29 to 17 and, over the course of a year, she battles a rare form of cancer. The dramedy is told from the point of view of her oldest child, David (Jesse Plemons), a comedy writer who has just relocated from New York to Sacramento to help take care of his mom.

The movie starts at the end of the story, so it's not a spoiler to say that Joanne doesn't make it. In other words, you know what's coming: Over the course of the movie, viewers see, in excruciating detail, her health deteriorate. In the beginning, she is effervescent, and  Shannon uses her huge, contagious smile for maximum heart-warming effect. Joanne is irreverent but never mean-spirited and maternal without being sappy. She has a sweet relationship with her husband (Bradley Whitford) and kids. (Her daughters are played by Maude Apatow and Madisen Beaty.) She cracks a lot of jokes, tells silly stories, jogs around the neighborhood and hosts parties. But before you know it, she can barely move without vomiting and she can't speak above a whisper.

Incidentally, Shannon also starred in a cancer dramedy at last year's Sundance, "Me and Earl and the Dying Girl." (If there's one thing that's even more prevalent at Sundance than comedians playing against type, it's cancer movies.) But this is more of a breakout role, and the actress makes an impact.

"Other People" is the autobiographical feature debut of SNL writer Chris Kelly, and his other job explains the movie's great strength: its comedy, despite the subject matter. Shannon is obviously a natural in that department, but Plemons also shows off some acting muscles he hasn't flexed before. The actor known for dramas — "Friday Night Lights," "Black Mass" — has spot-on comic timing. And all the absurd and buoyant moments make the touching moments all the more poignant. So when Shannon stops cracking jokes long enough to say, "all I ever wanted was to be a mom, and I got to do it three times," well, good luck trying to hide the tears.