Cats and animals know when they are dying and their instinct is to hide away. The day my cat precious died she hid behind a cabinet that I would never would expected to look. The only reason I looked there was cause I heard her cry. When she got sick she would ball up in the corner of a closet usually. Whether they cry out depends if there is pain. If they are just weak/nauseas/in shock then they are silent. But if there is something causing them pain then they will wail. I remember when my big guy Wolfy had urinary blockage for a day he was wailing. The bladder pain had to be aweful. Thank God he is healthy now.