The visual illusion called the Hermann (Hering) grid:

A. can be completely understood based on the receptive field properties of ganglion
B. cells is likely to result from operations at many stages of visual processing
C. is closely related to the scintillating grid illusion
D. has no explanation based on retinal processe

Bc they get tired from playing with other kittens

It depends on the surface of the levels. the rougher the surface, the greater is the frictional force. for rougher surfaces, you would need to exert greater force to move the object. the concept is that, you must overcome the frictional force in order to bring the object into motion. this is the reason why we add lubricants to the joints so they could easily move. this answer was on