The stapes, one of three tiny bones in the middle ear, is about 3 mm long: the smallest bone in your body. It's attached to the stapedius, the smallest skeletal muscle. When a loud sound hits, this muscle contracts to brake the stapes and protect the inner ear. It also kicks in when you speak, muffling your own voice.
Every day, your kidneys filter around 180 liters of blood plasma, about a bathtub's worth. Yet you only have about 3 liters of plasma, so it passes through your kidneys some sixty times a day. Over 99% of the filtered water is reabsorbed, leaving just one to two liters of urine.
A 70 kg adult is made of about 7 × 10²⁷ atoms, or seven billion billion billion. The observable universe is thought to hold on the order of 10²² to 10²⁴ stars. Even with the high estimate, you contain thousands of times more atoms than there are stars in the entire visible cosmos.