Be Excellent To Each Other

I watched it in terms of the Babadook being the son's materialisation of the mother's grief: how he was trying to protect her, building up an arsenal to try and fight what I guess what the manifestation of her depression and the barrier that it put up between the two.

exploration of the manifestation, evolution and coping mechanisms of a child's reaction to grief, depression and I guess mental illness

I really think you're onto something there. My interpretation, after reading your comment, is that all along she's been succumbing to these psychotic episodes and terrifying/abusing her child, though she always snaps out of it and realizes what she's done1. So being a children's book author and someone that does genuinely at times seem to love her child, she decides to create a book to try to provide him with an explanation a child might understand2. Because when it comes down to it, no kid Samuel's age is ever going to understand or even be able to come to grips with the fact that his Mom, at times, actually wants to kill him. So to protect him, she convinces him that it's actually a monster that's making her act that way. This explains why he's able to continue loving her unconditionally and retain some semblance of sanity. It also explains why he seems so practiced at combatting his mother when she finally attacks him (because she's done it before). He believes it isn't actually his mother doing these things, but it's the Babadook causing her to do them, so he can continue loving her and confront the abuse like he might confront a monster - something easier to understand than psychosis and clinical depression.

I, like others, found it odd and somewhat anticlimactic that she "defeats" the Babadook by screaming at it, but thinking back I interpret this as both a show she puts on for Samuel and also a psychological and physical release for her (as we all know a good scream can provide). It's interesting to note that this happens immediately after Samuel is thrown into the wall a few times by whom we can assume is his mother. Looking back on the scene, it's a powerful moment. Her maternal instinct defeats her psychotic tendencies caused by her crippling depression. In that respect, it's actually an extremely powerful scene and far more meaningful than traditional horror film climaxes. She needs to convince Samuel that the monster was real, she has finally confronted it, and that she's locked it in the basement where it will never fully go away, but be contained and managed day by day (just like real depression).

So back to the worms - why does she have Samuel collect worms for the Babadook? You had it right, @cypripediums; it's something a child might think a monster would eat. Which fits the narrative above perfectly. She is perpetuating the fantasy of her battle with the Babadook by telling Samuel she needs to feed it worms, because it's something Samuel can understand and continue to contribute to3. The truth is that she isn't actually feeding anything worms down in the basement, she's looking at all her husbands stuff - stuff she used to keep locked away and not confront. Just like with any mourning process, there are good days and bad days, and she explains this to Samuel by saying that Babadook was "quiet" today. This actually means she was able to let the sorrow of nostalgia wash over her and absorb it rather than let it overwhelm her and trigger another psychotic/depressive episode.

This movie reminded me a lot of Fight Club (obviously) and What Dreams May Come. It's a fantastic, beautiful, and horrifying view into the world of depression and psychosis.

Additional thoughts that popped into my head as I wrote my comment above:

1 - It sends a chill up my spine to realize the way she tries to make up for her abusive episodes in the typical way that abusive parents do; offering to take them to their favorite restaurant, letting them order as much ice cream as they want, allowing them to stay up past their bed time, etc. It's even creepier to realize she's been neglecting her kid so badly that he's starting to starve.

2 - The book seems to just appear in Samuel's room, and he chooses it on his own, but she was the one who made it and put it there. She even puts her own face in it. She's smart in this regard because he is able to come to his own conclusions that it's a monster causing her to act that way. But it's clear how much distress it causes her to even confront her inner demons in this childish form because she can't even make it through the book with Samuel. She promptly tears it apart because she wants to deny her issues. In a moment of lucidity not portrayed in the film, she pieces it back together, continues working on it, and predicts (accurately) that left un-checked, her depression will result in her killing everyone she loves including herself. The book as much a coping device for her son as it is a wakeup call for herself. When she finally burns the book, it signifies she has completely given into depression, and obviously what follows is her killing her dog and attempting to kill her son.

3 - It's interesting to note that his contributions are completely ineffective, including his home-alone style attacks, as you might expect for a victim of child abuse. But it empowers Samuel and also shields him from a truth that's too horrible for any child to confront - his mother resents him and at times wants him dead.

I dismissed the monster from the start, and kept exclaiming how everything about the monster could be explained as her being mentally ill all the way through. If it turns out that the 'twist' as such that it was her own depression and stuff all along, then I kind of already got it, which perhaps detracted from my enjoyment of it as a horror film.

Although I did like the fact that you thought it would be the kid who was 'possessed' when actually it was the mother.

And he would have died from adamantium poisoning the moment his mutant power was taken away

He never totally lost his mutant power; it was just being suppressed.

In the comics when Magneto ripped the adamantium out of him (in Fatal Attractions, I think), his healing ability went into super-overdrive, and Professor X told him that was because his healing ability spent 99% of it's time making sure he didn't drop dead due to adamantium poisoning. Even if it was only slightly diminished, Wolfie* be toast.

*That Wolfie, at least. When it was put back again they'd improved the bonding process so (like with Bullseye), having Adamantium inside you is no longer deadly, and Wolverine kept his "heal faster" ability.

Inconsistencies in the medium of comics and the adaptations thereof? Utterly shocking.