Slip of the mouth instead of a slip of the tongue?


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.)_




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".




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".

