Motion in a two dimensional, static space like in graphic comics are most of the time implied using implied lines, scaling, cropping, repetition, overlap, rotation, and/or shape or a combination of any of these techniques.
In the visual example I provided above you can see these techniques used throughout the comic. The comic has two basic things being repeated as the subjects of the story, the toaster/toast and Garfield. You can see the movement of the toast bouncing around the house through the use of the line following it and the implied movement as the toast moves in and out of frame. The implied sounds throughout the comic also add to the narrative that the toast is breaking things and bouncing around the house. You can also see movement in the characters like Garfield, as he reacts and dodges the piece of toast, and Jon as he runs away from the toast.