muscles / mussels are similar-sounding terms with different meanings (referred to as homophones). To better understand the differences, see below for definitions, pronunciation guides, and example sentences using each term. 👇
muscles: (noun) one of the contractile organs of the body. (noun) animal tissue consisting predominantly of contractile cells. (noun) authority or power or force (especially when used in a coercive way). (verb) make one's way by force.
mussels: (noun) black marine bivalves usually steamed in wine. (noun) marine or freshwater bivalve mollusk that lives attached to rocks etc..
muscles: m·AH·s·ah·l·z
mussels: m·AH·s·ah·l·z
(Examples are Wikipedia snippets under the CC ShareAlike 3.0 license. Definitions drawn from WordNet.)