Okay, so this is another ick for a letter. But other than ugli fruit, with which I am not familiar, I couldn’t come up with something beginning with U of any great significance and with a distinct odor.
Urine isn’t something people normally talk about, but physicians look at it for content (red and white blood cells, salts etc), color, and odor. Forensic technologists would do the same.
Urine normally doesn’t have a very strong odor, although some food can change urine odor: asparagus is a big culprit. What people are smelling when they eat asparagus is the breakdown of a sulfur compound called methyl mercaptan (the same compound found in garlic and skunk secretions). But a strong ammonia-like smell might indicate the presence of infection or kidney stones. The urine of a diabetic can smell sweet, which is why long ago doctors actually tasted urine to make a diagnosis. But urine can also have a strong smell if a person is dehydrated, because the kidney will retain water, and the urine will have higher concentrations of filtrates.
Urine gets its yellow color from a pigment called urochrome. That color normally varies from pale yellow to deep amber, depending on the concentration of the urine. Darker urine is usually a sign that you’re not drinking enough fluid, while pale urine indicates you’re drinking a lot of fluid. Or you could be taking a diuretic, which forces the body to get rid of excess water.
Urine can take on lots of other colors: some drugs turn is green or blue, carrots can tint it orange. There is also an inherited disease called porphyria, which is a malfunction in the body’s synthesis of a complex molecule called heme, the oxygen-carrying molecule in your blood. In this case the urine is the color of port wine.
Just one more comment on this unusual topic: urine is sterile and in the absence of clean water to wash a wound, urine can be used. This was a normal procedure during the Civil War.