Mom has a bruise; dad's hand seems a little stiffer -- you might notice something before it turns into a bigger problem.
It's hard for some people to admit when their bodies are failing them in little ways, so you might need to press a little bit for information. When did they notice the symptoms? Has this happened before? How often?
If dad is sore from falling down and it seems like he's been falling down a lot, an investigation is needed. It could be an ear infection, a medication side effect or just plain clumsiness. Mom's bruises could be explained by anticoagulants, or it could be a sign of something else going wrong. You won't know until you ask, and you can't assume that someone else is cataloging these symptoms as lovingly as you are.