Is it true Some irregular nouns change their vowel sound to form the plural?

Yes, that's true! Some irregular nouns change their vowel sound to form the plural. This is one of the quirks of English grammar.

Here are some examples:

* Man -> Men (The vowel sound changes from a short 'a' to a long 'e')

* Foot -> Feet (The vowel sound changes from a short 'u' to a long 'ee')

* Tooth -> Teeth (The vowel sound changes from a short 'oo' to a long 'ee')

* Goose -> Geese (The vowel sound changes from a short 'oo' to a long 'ee')

* Mouse -> Mice (The vowel sound changes from a short 'ou' to a long 'i')

These changes are mostly based on historical language shifts. The modern English language is filled with inconsistencies from its Germanic and Norman-French roots, making some plurals seem illogical.

It's worth noting that not all irregular nouns change their vowel sound. Some, like "child" -> "children," change their ending entirely.

This is just a small example of how English grammar can be surprisingly complex and sometimes illogical. 😅