Less surface area that you are touching, and also, you can see that the corners are cooler than the rest of the object.
Yeah but why do the corners get cooler?
This is only a guess, but, material in the corners is closer to more surface area so loses heat more quickly
More surface area?
If you think of it like a bunch of cells like minesweeper, where the temperature differential is a function of #of neighbouring air cells - corners are going to cool much faster!