Toaster mechanism. Loaf of bread placed on flat metal horizontal plate just above Gromit's eyes, leaning against the angled part that sticks up.
When fired, an arduino controller starts a motor that moves the angled part to the right, shoving the slices of bread past the angled 2x4 and out to the roller, which then peels a slice off the stack, which falls down the hopper to be held in front of the flames. After a preset amount of time, the arduino opens the trapdoor at the bottom of the hopper allowing the toast to fall out, hit a crossbeam, and land on a plate.
To the right of Gromit's head, past the angled 2x4, you can see the sides of the hopper and the shadows they cast; one on the left curves down from the roller, one on the right sticks straight up and acts as a backstop.