A couple of observations and comments:
1) You clearly haven't seen very many good magician's tricks. I was obsessed with magic tricks when I was younger and learned a lot of basic moves and techniques. But even with that there are some really, really simple tricks that use very simple props, or no props at all, that seem impossible and that I have no idea how to do. So when you say "In my mind there was simply no way you could _________" all I see is a huge red flag. It's called the Argument from Personal Incredulity, and it's a blatant logical fallacy. Someone who is not overly familiar with magic tricks, as I think might apply in your case, can see no way this effect could have been achieved without the claim being true. Someone who is moderately familiar with performance magic, on the other hand, can imagine quite easily that it could be the result of an illusion.
2) As for your "straining, curving, living thing" diving at the ground, I have to say, I'm shocked and the credulity of this statement. You think you can't make a branch held at two points bend and curve? Very small muscle movement is all it takes to make a freshly cut (and therefore flexible) branch move quite a lot, so it could seem like the branch was moving while the hands holding it stayed still. Combine that with the fact that it's been some time since this happened, I'd say it's entirely likely that you saw either an ideomotor effect or a skilled performance, and exaggerated it in your memory to the point where you remember it in a very dramatic light. Like I said, I used to study magic, and a huge amount of that is knowing how to take advantage of the remarkable human ability to remember things that didn't actually happen, or misremember things from how they really went down.
3) Just for the record, skeptical and cynical are not sister mindsets. I am so sick of people equating them, as I am actually quite idealistic on the whole, while also maintaining a healthy skeptical outlook. Skepticism only seems like a downer attitude when it pops someone's bubble by pointing out something they really want to be true isn't actually, and they get all petulant and bent out of shape about it.
It is funny you mentioned magician's tricks, though. You know, there's a reason there's so much overlap between skeptics and magicians. It's because magicians know how easy it is to do "impossible" things, and don't accept claims based solely on how something "appears" to happen.