Here's why:

* Mechanical weathering: Animals use physical force to break down the rock. This can be done through:

* Scratching and digging: Animals like rodents use their claws and teeth to chip away at the rock.

* Burrowing: The constant movement and pressure of the animal's body within the burrow can gradually erode the rock.

* Chemical weathering: While chemical weathering plays a role in the long-term breakdown of rock, it is not the primary force in the creation of animal burrows.

* Some animals may create burrows in rock that is already weakened by chemical weathering, but they are not directly responsible for the chemical processes themselves.

Therefore, the creation of animal burrows in rock is primarily a result of mechanical forces.