My Dad still has some slight problems with his memory after his brain surgery years ago. He will on occasion mix up words. It is usually quite subtle and if you aren't paying attention you might not even notice. However, he recently called my Brother to tell him that our Aunt had an accident in her wheelchair. Somehow it locked up on her and she got thrown out and broke a lot of bones. She's been in a wheelchair for many years so you can imagine what my brother was thinking when my Dad told him "Aunt Barbara is in the hospital, she got thrown off a horse." Chris was all, "What the HELL was she doing on a horse?" My Stepmom in the background screaming "A wheelchair Mark, a wheelchair." the whole time.
I myself have learned to pay close attention to what he's telling me. However, I chose to get directions to my brother's wedding from him a few weeks ago and that resulted in me going to the wrong town entirely.