i know this is not to do with what we say to cats, but a display of how they understand what is happening.
I suffer from seizures and my cat will know when i have had one and she goes to fetch my partner to let him know i have had one.
He knows she has gone to get him as she will go into him and then run straight back to me.
There have also been times when i have been on my own and i have woke up after a seizure and my cat is there watching me and then she will comfort me.
She also always comes to comfort me if i am crying.
There are times as well when i will be talking ot her and she will answer back so i definately think they understand us