Tiger also has its own meaning, which makes the parsing even harder.

Both 'tiger moth' and 'bat sonar' are noun phrases in which the first word is not the actual meaning of the phrase. So you have two of these weird noun phrases, topped off by ambiguity about the verb ('jam' vs 'bat').

Very tricky sentence to wrap your head around!

> Both 'tiger moth' and 'bat sonar' are noun phrases in which the first word is not the actual meaning of the phrase. So you have two of these weird noun phrases

That's not weird; it is the norm for English by a ridiculous margin. We do have some left-headed compounds ("pickpocket"), but they are very noticeable exceptions to an extremely strong rule.

Surely 'pickpocket' is that way because (there) 'pick' is a verb, not a noun? Like.. 'roast potato' or 'tryhard'. (To deviate way off course, isn't it also odd we don't say 'roasted potato', or 'roasted chicken', etc.? Or not in that context anyway, only if it was something like 'mashed or roasted?')

> Surely 'pickpocket' is that way because (there) 'pick' is a verb, not a noun? Like.. 'roast potato' or 'tryhard'.

No, the normal thing to do in modern English is to say "pocket picker"†, where the head of the phrase comes after the modifier. As you note, the other order remains possible in non-archaic forms ("tryhard", "kiss-ass"), but it is unusual.

"Roast potato" is already right-headed; it is a kind of potato, not a kind of roasting or an entity characterized by its practice of roasting.

† That is, the normal way to express this kind of concept, not the normal way to express the particular concept of a pickpocket, where a conventional word already exists.

Yeah ok roast potato was a bad (not a) example, I got hung up searching for a verb+noun one and lost track.

'pocket picker' illustrates my point though, you swapped the verb for noun form, and it became the other way around.

'kiss-ass' is the same again, or at least it arguably is. (And I would argue it: it alleges a person to be one who 'kisses ass', not who is the kiss on the ass itself.)

> 'pocket picker' illustrates my point though, you swapped the verb for noun form, and it became the other way around.

No, "pickpocket" is already a noun, and it means "pocket picker". Just like "kiss-ass".

'picker' compounded in 'pocket picker' is a noun, and 'pick' compounded in 'pickpocket' is a verb.

'kiss' ...

Suppose you want to describe someone by the action they perform. There is a normal way to do this, and "pocket picker" is an example of it.

There is also an extremely marked, almost-never-used way to do it, and "pickpocket" is an example of that.

What are you trying to say?

Sorry, you're right, they're not independently weird, but they're weird in this context.

Also, while they're not weird for a native speaker, a lot of other languages would also mark the adjunct or head noun somehow to remove any ambiguity.

I also had some fun thinking on a tiger moth jam, and how that may have batted a sonar.

Ah, garden path sentence! What a great term. I seriously had to read the title a couple times and thought initially it was an article on passphrases.

At first read I thought the title was a secure password example along the lines of "correct horse battery staple":

https://xkcd.com/936/