Water has a very high surface tension because of the strong hydrogen bonding between water molecules, which allows the pepper to float on top of the water. When a small amount of soap is added it forms a monolayer on the surface. The monolayer spreads away from the point of contact causing the pepper to move to the edges of the dish.
When dry ice is placed in warm water it sublimes very quickly forming a large amount of carbon dioxide gas. When a bubble is placed over this the bubble grows from the pressure.