the misunderstanding was due to the incorrect use of the plural form of the word “brownies”.

there was misunderstanding because “I left you four Brownies” needs another preposition.

the misunderstanding was due to the incorrect use of the word “left”, which is not a verb.

the misunderstanding was due to the improper use of the homophones “four” and “for”.

there was misunderstanding because the character thought that Brownie was a person.