Tunneling critter is a term used to describe animals that dig tunnels underground, such as moles. The four-letter word for this type of animal is 'MOLE'. Moles are small mammals that live in burrows and feed on insects, worms, and other small creatures. They have powerful claws and sharp teeth that help them dig through soil and create intricate tunnel systems. They are found in many parts of the world and can be beneficial to gardens and farms by aerating the soil and controlling pests.