When a human being stops eating due to illness and decline at the end of life, it can often indicate that they are ready to give up the fight. When one is helpless, frail, disabled and infirmed, they must rely on someone else to meet their basic needs. Sometimes the only control one has at this point is to clench the teeth and refuse to eat.
So many people who are caregivers don't understand this. They force feed or think that the patient is being uncooperative or unreasonable. It is not true in every case, but often the patient is communicating in the only way they know how. Refusing food is the only choice they have. They are saying "Enough Is Enough".
Us animals often do the same thing. This is one of the clues for you, of knowing when the time is coming to help us on our way.