Center Embedding!

Check out this beautiful example (from a comment thread at Mark Fiore's site):

The dog the rock thrown into the pack hit snarls the loudest.

Isn't that gorgeous?

It's a perfect example of what textbooks for other languages remind English speakers of: you can omit relative pronouns in English - that is, the commenter could have said "the dog that the rock which was thrown into the pack hit snarls...". (I hope you wouldn't, though; that sentence is clunky.) But it's also deeply embedded.

The dog snarls the loudest that was hit by the rock that was thrown into the pack.

The dog that was hit by the rock (that was) thrown into the pack snarls the loudest.

Both of those avoid the second level of embedding; the first one has no embedding, and thus the information structure is altered. "Snarls the loudest" is the kicker here and should be last; that's one of the things embedding lets you do.

(You can, of course, restructure this sentence lots of ways, for instance "The dog that snarls the loudest is the one that was hit by the rock that was thrown into the pack" or even something like "When you throw a rock into a pack of dogs, you will hit one and that one will snarl the loudest". )

ps - But wait! Isn't it a rule of English that

when the relative pronoun is the subject of a relative clause, it has to be included. (source BBC Learning English)

So how can we say "the rock thrown into the pack"? Isn't "the rock" the subject?

Yes, it is. But here we have a "reduced relative", which is made by omitting not only the relative but also the aux (the part of the verb phrase that carries tense and number), here the was of "was thrown". That turns the relative clause into an adjectival phrase, so it can modify the subject of the original clause and turn one entire clause into a noun phrase instead - thus densely compacting the sentence. Note, too, that if the verb doesn't have a complement, this new adjectival phrase can precede the noun (in effect, becoming an adjective):

the dog hit by the thrown rock snarls

In fact, note that in this compacted clause, "hit by the rock" is also a reduced relative; you could say "the hit dog". Other languages (Russian and Ukrainian, for example) can say "the thrown into the pack rock," or "the hit by the rock dog," or even "the hit by the thrown into the pack rock dog" - and how's that for embedding? It's helped by gender and case endings on the adjectivals, of course

Where in English we have three bare nouns

pack rock dog

in Russian we'd have

pack-accusative rock-instrumental dog-nominative

with matching endings on the participles and it would all sort out nicely

But English puts such complex (or heavy) modifiers after the noun regardless of whether a verbal form is involved:

a big house
a big enough house
a house big enough for my family

Ah, syntax. It's so much fun.