I have been doing a research on the subtitle translations of the American Tv show called "It's Always Sunny in Philedelphia" and faced an instant where Frank mentioned having a mind as sharp as a thumbtack. I know that there are idioms as "having a mind as sharp as a tack/razor/steel trap" along with the old ones like "as sharp as a needle or thorn". However, I have never heard "having a mind as sharp as a thumbtack". Although "as sharp as a thumbtack" and "as sharp as a tack" sound similar, if the native speakers have never heard of the idiom "as sharp as a tack", that would be an important detail to shape my work since it would suggest that Frank made up or changed that idiom. Thank you in advance.

  • (I'm a New Yorker) 'Sharp as a tack' is common; I have never heard 'sharp as a thumbtack'. Oct 20 '17 at 15:18
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    In that TV show, those characters play stooges who are always a little bit "off". It's a kind of malapropism. Oct 20 '17 at 16:28
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    Well you’re right since in that episode Dee makes fun of Frank for losing his mind due to old age and Frank tries to prove her wrong by saying “my mind is as sharp as a …”, but he cannot remember the rest of the idiom. So, at a later moment of that episode he screams “thumbtack” out of the blue in an attempt to say the rest of the idiom. However, learning that native speakers never use the idiom “as sharp as a thumbtack” proves that he is losing it. So, this has been very helpful. Thank you.
    – Ceren
    Oct 20 '17 at 19:02

Most people would understand the meaning of the idiom (with some thought), but as Jeff comments the shortened form is more widespread and would likely be your better choice:

Sharp as a tack


The idiom is "sharp as a tack":

Very intelligent and perceptive

I would imagine "sharp as a thumbtack" would be heard as a minor variation, unless the context of the show made it clear they were flipping it from a compliment to an insult.

Although if they were trying to flip the meaning I'd expect something much more obviously not sharp, or maybe something absurd like "sharp as a marble".

  • In my understanding, a (carpet) "tack" is a small "cut nail" like this with an extremely sharp point. A "thumbtack", on the other hand, looks like this (nowhere near as sharp, but the important thing is it has a large head you can push in with your thumb). Not that I believe anyone would specifically use sharp as a thumbtack to imply not actually as sharp as a real carpet tack. I'm sure it's just an uncommon / meaningless "copying error". Oct 20 '17 at 16:20

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