I do believe they know. 19 years ago, my mother got cancer and she had to have chemo once a month. Every time she would spend the best part of the week being ill in bed. One of our cats wuold spend the whole time lying beside her, she would leave the bed only to use the litter. Every time any member of our family was ill she would just curl up beside us. Just over 2 years ago my mother had a relapse and had to come to live with me. Maya has become really attached to her and would not leave her side. My mother tends to overdo things but every afternoon forces my mother to go and have a rest, she becomes a real pest if she does not go and lie down. As soon as she does she calms down. My mother says that both times managed to cope with her treatments because of the cats.