There's a video making the rounds, titled "Bringing a Fly Back to Life - Via Kabbalah!" It beings by showing a drowned fly floating in a cup of water. The person producing the video cites Rav Benayahu Shmueli (a disciple of Rak Kaduri and Rosh Yeshiva of Yeshivat Hamekubalim Nahar Shalom), who says that if one takes such a dead fly, and places ashes on it, it will come back to life. The person then carefully takes out the fly, puts it on the table, and scatters some cigarette ash on it. To the shocked gasps and exclamations of the onlookers, the fly returns to life! As the speaker explains, this is a kiddush Shem Shamayim, showing that the words of the Sages are true.
You can really see this on the video! Here it is (if you are reading this via email subscription, you will have to visit www.RationalistJudaism.com to see the video):
Okay, so what's going on here? First of all, the original source (or rather, the earliest rabbinic source that I know of) is in Shevet HaMussar from Rabbi Eliyahu HaKohen Itamari (1659-1729), also known for his work Midrash Talpiyot. However, he does not present it as some kind of kabbalistic insight. Instead, he just presents it as a fact of the world.
The fact that drowned flies sometimes come back to life was noticed by others, too. Benjamin Franklin wrote about it, as did others. A simple Google search shows that this phenomenon is widely known, with the slight variation of using salt rather than ashes to bring the fly back to life. The explanation of this amazing phenomenon is entirely straightforward.
Insects do not breathe through their mouths. Instead, they have tubes all over their bodies, called spiracles, via which they obtain oxygen. If the insect is submerged in water, the spiracles are blocked and the insect falls unconscious. But if you sprinkle salt (or ashes) upon it, this draws the water out of the spiracles, and the insect returns to consciousness. Of course, this is not actual techiyat hameitim; it does not work if the fly is actually dead.
Fascinatingly, this was guessed at by the one of the Moetzes Gedolei HaTorah. Rabbi Dovid Sperber (1875-1962) was a leading rabbinic authority in Romania who was appointed to the Moetzes Gedolei HaTorah of Agudas Yisrael. In his She’eilos U’teshuvos Afarkasta De’anya, vol. II, Orach Chaim 52, he discusses Rabbi Itamari's statement about the fly in light of the prohibition against killing insects on Shabbos. Rabbi Sperber asks whether it would be permissible to dispose of a fly on Shabbos by throwing it in a cup of water. He first reasons that although the fly can come back to life, this does not mean that one is allowed to kill it, just as it is forbidden to kill a person even if the murder victim is subsequently miraculously brought back to life. However, he concludes that although Rav Itamari speaks about the fly actually dying, this is not the case; rather, when the fly is in the water, it merely becomes inactive.
So, while there is something fascinating here, it's not at all miraculous, and it's not a demonstration of kabbalah, and nor was it even originally suggested to be anything of the sort. It's a simple observation of a known phenomenon with a perfectly reasonable explanation. The same, however, cannot be said for the second part of Rav Itamari's statement - where he says that if the flies are sealed in a jar of water for forty days, they turn into frogs!
שבט מוסר פי"א: זבובים שנפלו למים ומתו, אם תשימם בשמש ותשליך אפר מקלה עליהן חוזרין לחיותן, ואם תמלא צלוחית מים עד חצי' ותשליך בתוכה זבובים ותסתום פי הצלוחית עד ארבעים יום, מתהפכים הזבובים לצפרדעים.
Now, although Rabbi J. David Bleich claims that such things are not at all contradicted by reason, I beg to differ. Show me flies in a sealed jar turning into frogs, and I will give up on rationalism!
(Thanks to Rabbi Chaim Rapoport for sending me the sources)