if given a choice between heavy objects and light ones, solid and hollow ones, the crows will spontaneously pick objects that will sink over those that will float. They know how to pick their materials and will select the right option 90 percent of the time. This suggests that the crows understand water displacement, a fairly sophisticated physical concept, on par with the comprehension of a child five to seven years old. It also suggests that they’re able to grasp the basic physical properties of objects and make inferences about them.
