Final answer:
The application of pressure causes the two ice cubes to melt slightly where they are in contact. When the pressure is released, the water refreezes, joining the cubes together.
Step-by-step explanation:
When the two cubes of ice are pressed together, you increase the pressure on the areas where the two cubes touch each other. This increased pressure causes the ice to melt slightly, turning it into water. This is because increasing pressure lowers the freezing point of water, a phenomenon known as 'pressure melting'. However, when you release the pressure, the water refreezes, thus effectively joining the two cubes together. This happens because the conditions are still below the freezing point of ice, so once the pressure is taken away, the water turns back into ice, causing the cubes to join together.
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