Why does Rashi explain “למאי נפקא מינה” on חולין דף ח ע״א?

Question

The Bavli, Chulin 8 amud 1:

איבעיא להו ליבן שפוד והכה בו משום שחין נדון או משום מכוה נדון

As explained by Rashi, the g'mara is asking as follows: Suppose someone heated a spit and hit someone with it, hard. You might think the resulting wound is considered a שחין, because a שחין is the result of a blow. On the other hand, you might think it's a מכוה, because a מכוה is the result of the application of a heated object. (These — שחין and מכוה — are categories of wound in the laws of צרעת.) So which is it: שחין or מכוה‎?

The g'mara immediately counters:

למאי נפקא מינה

And Rashi explains the question:

באיזה דבר חלוק דין מכוה משחין דתיבעי לך

In what matter is the rule of מכוה different from שחין, that you're asking [whether a heated-spit wound is מכוה or שחין‎]?

I don't understand why Rashi explains this here. There must be hundreds of similar "למאי נפקא מינה" lines throughout the Bavli that have much the same meaning this one does—

In what matter is the rule of … different from … (that you're asking whether/telling that something is one of them)?

— and Rashi doesn't explain the question. (For example, Chulin 87 amud 1, "ליתן לו עשרה זהובים איבעיא להו שכר מצוה או שכר ברכה למאי נפקא מינה"; Shabas 20–21, "שעוה פסולתא דדובשא למאי נפקא מינה".) Why does Rashi explain it here?

Answer 1

From my own understanding of Rashi:

The Gemara chose to express the initial question by saying "Do we judge" this wound as a "blow" or "burn"??

As soon as the Gemara says "Do we judge", then the famous phrase of "L'mai Nafka Minah"? למאי נפקא מינה , is inappropriate (at least according to its usual usage).

The average student of the Talmud is used to seeing L'mai Nafka Minah? (What would be the practical case of a difference?) as used when the Gemara admits (or has no argument with) the statement offered. Rather, the Gemara accepts the statement just offered; and then asks anyway: "So even if I accept what you just said...in what case would there be a practical application of a difference in Law?

Here, The Gemara just said that there is such a thing as the "Din" or Law of a "blow" as opposed to the law of a "burn". If so, then we would not ask "what practical difference is there" because the obvious difference is if we judge the heated spit injury under the law of a blow or burn! So we should not be asking "L'mai nafka minah" at all over here!

So Rashi is explaining to the student of the Talmud that here is an exceptional case of usage for the question "L'mai nafka minah"?

Here the phrase is used as a direct argument against what the Gemara has just tried to pass off as simple and accepted. It is actually a direct objection:

"Wait a minute Rabbis! What could possibly be the practical difference between any "law" of a blow vs the "law" of a burn?? In both cases, the perpetrator would be liable for the same damages anyway (as opposed to say for example, when a thief steals a sheep or an ox. One pays 4 times the sheep's value or 5 times the ox's value. By blow vs burn, there is no difference. There isn't even any difference regarding the laws of Tzaraas either (at first glance)).

Then the gemara had to explain itself that there is in fact a case where classifying a blow or burn makes a difference in law.

Since the average student of the Talmud would have been confused by this uncommon usage of "L'mai nafka minah", Rashi had to spell it out and explain it.

I hope this helps.