I'd like to start with a question from Harry Potter and the Prisoner of Azkaban (the 3rd book and movie):
Why did Harry Potter's "boggart" effect him like a "dementor?"
As background to the question, "boggarts" and "dementors" are both fictional magical creatures from the Harry Potter stories. Each one has magical powers that we learn about in the 3rd book.
Dementors are introduced in chapter ten, as Professor Lupin explains to Harry: "Dementors are among the foulest creatures that walk this earth... they drain peace, hope and happiness out of the air... get too near a dementor and every good feeling, every happy memory, will be sucked out of you... you'll be left with nothing but the worst experiences of your life...."
Boggarts are introduced in seven, as Hermione answers in Defense class: "(A boggart) is a shape-shifter... It can take the shape of whatever it thinks will frighten us most." As the story continues, the boggart proceeds to take the forms of whatever will most frighten the student closest to it. When Harry Potter faces a boggart in chapter twelve, it takes the form of a dementor, and, as dementors do, it causes Harry to relive the worst experiences of his life.
But this brings us to a question: Boggarts only take the form of whatever will frighten us, they don't actually become those things. The boggart facing the defense class didn't actually become Neville's grandmother or a mummy, it just looked exactly like them. So when Harry faces the boggart that looks like a dementor, why should it effect him like a dementor does?
Believe it or not, we can see a perspective on this question from the Torah. Obviously beggarts and dementors aren't real, but the Torah does talk about things that are analogous to shape-shifting creatures in Harry Potter. To ask a more general question: if something has the ability to magically take the form of something else, would it have the essence of that thing, or only the form of that thing?
In the Torah we learn of the manna ("mon" in Hebrew) that Divinely fell from the sky when the Jews were in the desert after leaving Egypt. The Midrash (Shmot Raba) says that the manna contained the tastes of all foods, and that it magically tasted like whatever the person eating it wanted it to taste like. Someone who wanted pizza would eat manna that tasted magically like pizza. Someone who wanted steak would have manna that tasted magically like steak.
Rephrasing our question from above, did the manna in the desert remain essentially manna, and simply taste like steak or pizza, or did it actually take on the essence of the pizza or steak? To explore this, we can consider a few discussions in Torah literature in which this distinction between taste and essence is important.
Suppose on Passover in the desert the Jews had taken manna and desired it to taste like matza, the unleavened bread eaten at the Passover Seder. Could they then have eaten this manna/matza at their Seder and fulfilled the commandment to eat matza? The Ritva commentary on the Talmud (Kiddishin 38a) describes the sequence of events when the Jews arrived in the Land of Israel after the forty years in the desert. Ritva says that the Jews ate manna until the 16th day of the Jewish month of Nissan, as described in the Torah, but that on Seder night, on the 16th day of Nissan, they ate matza made from new crops of wheat. (This is significant in the Talmud's understanding some of the Torah's laws about agriculture.) This implies that the manna could not be eaten to fulfill the Seder's requirement of matza, and that the Jews had to instead eat from the new wheat crop. We can infer from this that according to the Ritva the manna did not take on the essense of the food being desired, only the taste.
Other Torah sources, however, are of the opposite opinion. The Igra De'kalla (*) is reported to have been of the opinion that manna could have been eaten as matza, and the appropriate Blessings could have been said exactly as if regular matza were eaten.
Suppose someone took a piece of manna and desired that it taste like a cheeseburger, a pork chop, or another non-Kosher piece of food. Would the manna have the non-Kosher taste, and would the eater transgress the Kosher laws by eating it? This too is the subject of a disagreement among Torah authorities. The Chiddushei HaRim (*) (from the Gerrer chassidic dynasty) stated that the manna would not take on the forbidden taste, implying that the manna does take on the essence of the desired food, and that G-d prevented it from causing a transgression. But the Chida (*) stated that the manna could in fact taste like forbidden foods, and that it was permitted to eat it, the obvious implication being that the manna adopted the taste but not the essence of the desired food.
Like many areas of Torah literature, we're left with a Rabbinic disagreement over whether manna adopted the essence or just the taste of the food that was desired. While Rabbinic disagreements in practical areas are most often decided conclusively, since people need to act in accordance with one of the opinions, in non-practical areas of Torah thought there is often no conclusive answer. This appears to be one of those times.
Returning to our original question, it appears that the Chiddushei HaRim and the Igra De'Kalla are of the opinion that something that magically takes on the form of something else also takes on the actual essense of the thing. This is analogous to Harry Potter's boggart effecting him like a dementor. But the Chida and the Ritva seem to say no, taking on attributes of something doesn't mean taking on the essense of the thing. In the analogy to Harry Potter, this would lead us to conclude that Harry's boggart should not have effected him in this way.
Obviously these analogies are meant for fun, to make us think about Torah concepts in new and interesting ways, and should not be taken too far. (See the preface of Harry Potter and Torah for more on this.) That said, we have seen some Torah thought that seems very analogous to the issue in Harry Potter, and this Torah thought is also something that many of us have not previously considered.
So if anyone reading this comes across some manna right before Passover, I do not suggest eating it as matza at your seder. But if you're reading Harry Potter (or anything else), and some interesting thoughts come to mind, remember this: Somewhere, somehow, Torah literature has discussed the subject.
Torah sources marked with an (*) are those that I have not yet seen in the original, but were quoted in secondary sources. For more in-depth coverage of this subject, see the fascinating article in English by Rabbi Ari Zivitofsky, "Bacon bits and non-Kosher taste."