is this movie appropriate for a 9 year old

I would say this movie should be O.K. for a 9 yr. old. There are a few words used but it's kept to a minimum.
Also, keep an eye out for the absolute most rediculous bit of dialog ever written. As 2 guys get out of a truck and start walking into a wooded area, one guy says "what the ---
I'm not going to finish the line here, just watch for it and when you here it you'll be on the floor roolin'.

There's no nudity though I think there might be one or two bad words.

As for if it's scary that depends because I saw this when I was six or seven, and I thought it was but at the same time I didn't think stuff like Nightmare on Elm Street was scary so it might be an opinion thing.

That and the only really scary scene I can think of is the infamous "money shot" scene where the plant sprays that white stuff on the guy, and he comes out as one of the plant monsters but the happens quite early in the movie, and the rest is kind of slow.

Me thinks you can do better then this Invasion of the Body Snatchers ripoff, in fact, why don't you let your son watch that instead?

Its one of those flicks that didn't age well at all and the FX are really laughable. I recommend Monster Squad or Gremlins over this crapfest.

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Im gonna punch you in the cooter, I swear to God!