They explained it..or in a simple way, the cause was from the plants. What a corny idea. He should have just left it as a mystery but given some signs to look for, something in the wind and having to do with trees and plants then leave it at that. But the whole thing about all the plants talking with each other and going after people was like I said, corny. He should've had it end after a rainstorm as if washing it away, something like that.