Can dogs tell when a person is sick?

Yes and not only dogs, but cats too. My husband just got over a lengthy illness. We have 2 dogs and a cat. Tootsie is part Bichon Frise and Booker T is a Cockapoo and our cat Molly is a tabby. Usually they are always playing and goofing around, but all during my husband's illness they were very quiet. Not only that, all three would often get on the bed very gently, sniff him every so often (making sure he was OK) and they'd take turns doing this. Then lay for hours with him. When I was in the kitchen one day and my husband was in the front room Molly came in meowing furiously and touching my leg. I was busy and told her to leave me alone. Then the two dogs came in jumping up on me. I then realized something was wrong and I followed them into the front room. There was my husband on his knees holding his stomach in great pain. I rushed and called the ambulance. The front door was wide open so the ambulance attendants could get in quickly and not once did my two dogs or cat try to run outside into the yard. In fact, they snuggled around my husband and when the ambulance attendants finally came they moved off to the side and were very quiet. My husband was admitted into ER and spent 9 days in hospital. Of course I went up every evening and when I got home my three pets were ever so gentle greeting me (usually they'd go crazy when I get home) and then would just snuggle with me. If I cried, the look on all three little faces was a solid 'Don't cry, it will get better.' The three of them would just cuddle right up to me and if I did something around the house they would follow me everywhere. They were perfect while my husband was ill, but once he got well boy, they made up for lost time! LOL You bet animals know and they are used to help people that are blind, can't hear, have seizures, strokes and a myriad of problems. Cats and pigs are also very smart and look after their owners. Some days I prefer my pets to humans! They don't jiggy you, lie, cheat, steal, backstab, take their bad moods out on you and are always loyal and love you for who you are.