The Taking of Deborah Logan (2014)

Hey, has anybody seen this? I saw it a few days ago, and I think I need to watch it again. I mostly liked it, but I am not sure if I'm understanding what happens. I think it might be giving the audience credit for having brains, so we have to figure a few things out for ourselves... I %$^&•?#@!ing hate it when movies do that. Seriously, I mostly do like it, but I am unclear on a few things. Spoilers follow...
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It seems like there are at least two possessions happening at the same time, to Deborah, while Deborah is also losing her mind to Alzheimers, at the same time. What a fortunate woman she is.

She is getting possessed by that Desjardins guy (which they pronounce in a strangely Spanish way for a French name... they say it Day-har-deen," as opposed to Day-ZHARD-DAN... but that's not important right now). Anyway, it seems quite clear that she is getting possessed by him, but she is also turning into a snake. Does that mean she is getting possessed by some kind of ancient Monacan snake god? Can she be possessed by both of them at the same time?

Also, the little girl at the end is definitely possessed, but I did not see any snakiness about her. I think she is simply possessed by Desjardins. Did the snake god stay inside Deborah's Alzheimer's ravaged brain? I guess it's possible.

Anyway, I'm pretty sure I need to just watch this again, and pay better attention. If anyone would care to clear any of this stuff up for me though, I would appreciate hearing your thoughts.