Yes, dogs can technically look up, but only so far. Because of the way their spine and neck are built, they are physically limited in how high they can look. After a certain point/angle, it's just not possible. This angle is higher when the dog is sitting than when it is standing. A dog cannot look directly upwards (without, say, lying on its back). Dogs also have more limited motion in their eyeballs than human beings do. Most people answering this question simply think of the fact that dogs can turn their heads up to look at people and don't consider whether or not their actual eye is moving up.
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