The movie doesn't sort out how the beaver reduces Walter's family -- especially Meredith -- is reduced to reinforcing his worldview.
Meredith (Jodie Foster) is at a turning point. She must do something about her husband, the odiously named Walter Black (Mel Gibson), who's been making her life and her children's lives increasingly miserable. He's "hopelessly depressed," sleeping all day and night, unfixed by the many doctors he's seen or pills he's been prescribed. Nothing has helped, you learn during a montage at the start of The Beaver. "His depression is an ink that stains everything it touches."
That stain is rendered variously and unsubtly. Seven-year-old Henry (Riley Thomas Stewart) is feeling invisible at school (a feeling exacerbated by the fact that his mother repeatedly drives past him when she comes to pick him up) and high school senior Porter (Anton Yelchin) been writing papers in exchange for money from his classmates, pitched with the promise that he can mimic their "voices." You get what this means because it's so painfully obvious: neither son has an identity he might call his own, much less a dad who acknowledges his existence or a mom who has time to spend with him.
They're no longer the family who posed smiling for Christmas cards or vacationed at the beach. Now dad sleeps all day and Meredith holes up with her MacBook Pro late at night, conducting conference calls with Tokyo-based counterparts. When she's not driving past Henry at school, Meredith is arguing with Porter, who fumes and blames her for letting Walter hang around for so long. You see that Porter suffers awful pain, that he spends his evenings smashing his head against his bedroom wall until he literally puts a hole through it, exposing pink insulation and his own freaked-out eyeball as the camera pulls out from the exterior. You also see that mom has somehow missed this pounding each night, one of the few plot points this movie doesn’t lay out explicitly.
As heavy-handed as these indications of damage may be, they do suggest The beaver has at least a nominal interest in the effects of mental illness on family members, how a wife and kids might cope with a man who's "gone missing." Thus it's a disappointment when the film turns away from the family and to Walter, whose illness begins to look awfully unserious once he takes up with the beaver.
As most everyone knows, the beaver is a puppet, in particular, one who seemingly calls to Walter from within a green dumpster. Once he has his "arm up its bum," as the beaver puts it, Walter is transformed. Now he has a material incarnation of his own self-loathing. The puppet instructs him how to be an attentive dad (Henry is thrilled to converse with the beaver), a decent lover to Meredith (who's slightly less thrilled when the puppet literally lies between them while mimicking Walter's post-coital heavy breathing).
If these interactions are odd but maybe understandable (as wife and child are meeting Walter's damage with their own), Walter and the beaver's appearance at the toy company where he's CEO (a position inherited from his own, hard-to-follow father) is just preposterous. Here the mostly anonymous employees (including a VP played by Cherry Jones) look briefly skeptical that their new production schedule is ordained by a puppet, but they're soon hard at working, rolling out inexplicably popular “Mr. Beaver Wood-Cutting Kits” and making lots of money -- for the boss, anyway. Yes, corporations are crass and greedy at every possible turn.
Walter's success as or with the beaver (he appears on TV, the gimmick of the beaver set opposite Jon Stewart and "Fresh Air"'s Terry Gross, who delivers the movie's most resonant joke, wondering why he needs a puppet on a radio show) suggests to outsiders that he's en route to a recovery (until, of course, that collective fantasy is revealed as such and those outsiders as exploitative know-nothings).
As if to show it doesn't trust viewers to get the point -- say, the tragic consequences of ignoring mental illness -- it delivers a parallel plot in Porter's experience. Not only is he denying his own "voice" and banging his head through the house, he's also intermittently distracted by a developing relationship with class valedictorian Norah (Jennifer Lawrence). He's crushing on her when she passes him in slow motion wearing her cheerleader's uniform (wasn't this cliché already tedious in American Beauty and before that, quite undone in Twin Peaks?), and ecstatic when she solicits his services for her graduation speech ("I hear you're really good at making yourself sound like [clients]," she says, "getting inside their heads").
Of course their romance needs Norah to be vulnerable too: when Porter suspects this overachiever is making fun of him, she pulls out 428 draft pages she's been working on (who is this high school student who carries such daunting weight in her backpack?). But as soon as it starts -- when they agree on a price -- the relationship becomes a too obvious way to compare Porter and Walter (literally, Walter and Porter prepare for "dates" in a panning montage that matches their behaviors). Trying to speak through and for others, unable to imagine others as individuals, the boys turn to girls for help and at the same time turn the girls away, precisely because they can only see them as extensions of themselves.
What the movie doesn't consider is why Walter and Porter would see their lives like that, why they'd be so typical as opposed to in any way original. Walter works hard to work out his depression with the beaver (to the point that it attacks and bloodies him in a way that too eerily recalls the stories concerning Gibson's many movie beatings, father issues, and self-destructions). But the movie doesn't do enough work to sort out how the beaver reduces Walter's family -- especially Meredith -- to a reflection of his worldview.