Actually, there are a number of animals smart enough to open their cages unless a key is the only way to open the cage. Apes, monkeys, parrots, crows, horses, even elephants and of course, dogs and cats. Not every member of each species has the intelligence or the will to open their cage. Many of these animals are very observant and learn to copy our actions. My German Shepherd, Quanah, learned to open doors by the time she was 6 months old. Needless to say, I keep them locked now. She can't reach the keys.