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This sentence is in my JLPT textbook:

> つい舌{した}がすべってしまい、うそがばれてしまった。

I thought that it meant something like, "with an unintentional slip of the
tongue, my lie was exposed." However, the sentence is marked as being an
incorrect usage of `すべる`, and it doesn't explain why.

I know that one can say `つい口{くち}がすべる`, which in English I would equate with "a
slip of the tongue," to accidentally say something one didn't intend to say.

In Japanese, is it only mouths that slip, not tongues?

_(A helpful answer would not only confirm this with a yes or no, but ideally
offer a little insight on how`口{くち}` and `舌{した}` differ in metaphorical
terms.)_
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2013-03-11T08:36:10.520
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question
word-choice jlpt
Slip of the mouth instead of a slip of the tongue?
Yes - it would seem mouths slip not tongues.

The book is testing your recognition of the expression 口が滑る, trying to throw
you off by inserting 舌. (Its probably a common technique for the other
questions you are looking at)

The best insight I can suggest for this expression is to look up 口 and 舌 in
the dictionary to see how they are used. 口 tends to be used more for
words/talking eg:

性格はいいけど口が悪い。

But it is not hard and fast. There are also expressions about speaking that do
use tongue:

舌がもつれて何も言えなかった｜I was tongue-tied

よく舌が回るね｜〔批判的に〕You really do [go on / talk].

But the main point for this book is to remember uses of 滑る
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2013-03-12T14:11:59.783
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Probably the reason the book highlighted this is that the set phrase in
Japanese, 口がすべる, is easily confused with the literal translation of a very
similar set phrase in English, 舌がすべる。

I don't think this points to an overall difference in the metaphorical uses of
口・舌 (see also the word 舌禍{ぜっか}), just one of many cases where caution is
needed. I don't know the book so I don't know if this is something they
regularly do - it would have been better if they'd added something along the
lines of "this is not the collocation you are looking for, try 口がすべる instead".
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2013-03-12T16:41:44.677
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answer