Do you know enough about your pets personality to detect a problem early on?
A pets behavior can tell you a lot about how they are feeling. If your dog comes up to you with a toy often and tries to play with you, she has a lot of energy that she needs to use; in other words, she's bored. If your rat stops eating and loses weight, his teeth may be too long and need to be trimmed.
However, there are plenty of behavior changes that should alarm you. If your pet who prefers not to be touched or engaged with suddenly begins to cuddle you, this may be a sign that she's sick. You should not be happy that it's suddenly warming up to you; be worried. If any animal begins to sleep a lot more than usual, that is a sign that must be taken seriously and should be taken to a vet for a checkup.
Physical changes should also be noted. If you pet your dog and feel bumps on it where there weren't any bumps before, it may be cancer. Cancer can take a pet's life very quickly after you notice anything wrong; even within a week.
Does your dog like snow, or rain? If he doesn't, and one day goes outside in the snow and begins to energetically dig within it, you should be worried and call for help.
Little personality quirks should be noticed and watched for, in case there's a sudden change. It could save your animals life when you see that it's acting abnormally based on it's own self.
What are some things that your animal does that is special?
My cat likes to be around people, even when she doesn't want attention. When there are people in the kitchen, she lays on the counter. If there's people in the living room, she finds a cushion to get comfortable on. However, she does like to find a quiet place to nap, usually in the front window or the window sill in my brothers room. If my brothers are out, she'll sleep on my parents bed, which is her favorite place to sleep.