What does the cryptic crossword clue "Mule is chewing cereal (6)" mean?

The definition is "cereal". The wordplay uses an anagram. anagram of MULE + IS = MUESLI; definition: "cereal" The answer is MUESLI.

Mule is chewing cereal (6)

Guardian Cryptic #27759 | 22 Down | 2019-03-04 flower