Plato's got the point, and I'd just like to add to the punch a little.
First of all, "unknown elements" in implants?? We already know all elements up to 114, I believe (and those heavy ones are all highly toxic). So I'd imagine the elements are very known. What I have heard rather is that the 'implants' have an intricate, layered structure. However, that does not impress me since all biological structures are intricate and layered. Made of metal? Well, our bodies contain plenty of minerals, including metals. In fact, as I vaguely recall, the so-called 'implants' aren't made of alloyed metal, and don't even exhibit isotope levels inconsistent with Earth origin. Though there may be others I haven't read about that are metal, as Plato points out there are plenty of ways those 'implants' could get embedded in soft tissue. Though last time I heard, none were found in peoples' *brains*??
As for why the alien 'devices' sound so primitive? I've got three alternative explanations. First: there is beauty in simplicity. Perhaps a truly advanced technology is the one that leads to the most 'primitive' design. Alternative: we made them up -- therefore the alien technology is only on par with our own. Another alternative: we could be seeing just 'shadows' of sophisticated machines, the bulk of which is hidden from us in other dimensions. Of course, there may be other possibilities as well...
Another neurological hint at 'abduction' experiences. During sleep our bodies go into what's been appropriately called "sleep paralysis". That is, the entire motor system is massively inhibited -- especially during REM sleep. One can readily see the usefullness of such a biological device -- because when it malfunctions people end up thrashing about and sleepwalking. But it can malfunction in a different way as well: people can wake up still paralyzed. Unable to move, that is. Don't think I'm making this up; it's a clinical syndrome. The paralysis eventually vanishes, but it does take a few minutes. During which time, people typically are in a whole lot of panic (when they are truly awake). Or, they may be only partially awake, and their inability to move translates into a nightmare. Abduction, anyone? One other thing: during sleep another protective mechanism kicks in -- the transfer from short-term memory into long-term storage is inhibited. Makes sense, since our dreams do not -- and if we remembered them we'd be very confused. That's why you normally forget the dream, even if you vividly remembered it just two minutes ago. However, if the dream was particularly traumatic, or you were woken up right in the middle of it, you may retain it in long-term memory. Again, could this possibly hint at 'abductions'? One question I'd ask 'abductees': can they regularly remember their dreams? If they can, then something's wrong with their sleep regulatory mechanisms.
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I am; therefore I think.