A muscle is a type of body tissue that contracts when stimulated to produce motion. Muscles help people and animals do things — like breathe, walk, blink, and eat. A mussel is a small shellfish, a type of mollusk, that attaches itself to underwater rocks and lives in colonies.

Humans have more than 650 muscles that act a bit like a construction crew taking orders from the brain to keep things moving — literally. Muscles build up when needed, repair themselves, and flex their way through life's daily grind. Muscles keep the heart pumping. The word muscle can also refer more figuratively to power, strength, or influence. Some cars with powerful engines are called muscle cars. Companies and politicians can use their muscle to do things like raise money or get laws passed. And although it's not polite, if you push your way to the front of the line, it could be said that you muscled your way there. The following sentences illustrate some correct uses of muscle:

I could feel the horse's muscles moving under her skin. (The Lions of Little Rock)

Beijing most recently published a map outlining its claims in August, underwriting its claims with maritime muscle that the Philippines cannot match. (The Washington Times)

Mussels can be found in both fresh and salt water. They hang out on rocks, never moving much. But don't let their laid-back attitude fool you; mussels work hard filtering water and keeping coastal ecosystems in check. The shells of mussels — called "valves" — are dark blue, black, or greenish in color and have an elongated shape. Inside the shell of a mussel is the edible part. Mussels are often steamed in a flavorful broth and eaten right out of the shell. Check out these examples of mussels in the wild:

He saw cod and sailfish and sardines, barrels of mussels and clams. (A Dance with Dragons)

When a 1,300-pound walrus showed up in Oslo last summer, lounging on piers and eating mussels, she became a beloved local delight and an overnight international media sensation. (The New York Times)

They look similar and sound the same, but to help remember the difference, think about all the things muscles can help you do, and use two s's in mussel since it has two shells.