Exact definition of 針千本 in the 指切り idiom


I'm trying to learn more about idioms and expressions, and I came across this
(which is apparently said when making a [pinky] promise):

> 指切拳万{ゆびきりげんまん}、嘘ついたら針千本{はりせんぼん}呑ます

Casting the first part aside, which is technically already a 四字熟語 for pinky
promise; the second part of "針千本呑ます" has gotten me confused. Looking up the
definition of the phrase on
[Weblio](https://ejje.weblio.jp/content/%E6%8C%87%E5%88%87%E6%8B%B3%E4%B8%87%E3%80%81%E5%98%98%E3%81%A4%E3%81%84%E3%81%9F%E3%82%89%E9%87%9D%E5%8D%83%E6%9C%AC%E5%91%91%E3%81%BE%E3%81%99)
returns _"swallow a thousand needles"_ for that section, however when I
searched [Jisho](http://jisho.org/search/%E9%87%9D%E5%8D%83%E6%9C%AC) for
"針千本" specifically, the word was defined as _"porcupinefish"_.

I understand that 呑む signifies an action of precisely _drinking_ or
_swallowing_ , in which case the needles would make more sense; but I can't
see how the verb 呑む can't be used in this sense in a somewhat symbolic manner
— not exactly having to "drink" the creature.

Which definition is the phrase exactly pointing towards? And more importantly,
_is there a reason behind it?_ Or is it just an unexpected coincidence?
Although neither ingesting needles nor eating porcupinefish would be an
enjoyable experience.




In this sentence,針千本 means thousands needls. Do you hear how japanese
pronounce this sentence? There is a subtle space between 針 and 千本.If 針千本 means
porcupinefish, the space should not exist.

