In addition to a food chamber, the burrow system also features chambers used for nesting and as a communal toilet. In addition, mole-rats dig deep, blind-ended tunnels they may use to escape enemies or to cool themselves; these tunnels may also function as drains in the event of flooding. Normally, the burrow system is not open to the surface, but is tightly sealed to provide protection against weather, extremes of temperature, and predators. Openings are necessary during tunnel excavation, in which a digging mole-rat loosens the soil with teeth or forelegs, pushes it beneath its body, and kicks it behind. When enough soil has accumulated in this way, the mole-rat backs up in the tunnel, pushing the soil behind it; the soil is directed out a side tunnel to the surface, where it is kicked out. With some species, the soil becomes compacted in being pushed on its way out, and may be seen emerging from the ground in a compacted core, like toothpaste being squeezed from the tube. With the naked mole-rat, the dry soil is vigorously ejected in a fine spray, creating the characteristic soil "volcanoes" that erupt at the excavation hole. An open hole, however, is an invitation to predators. Mole snakes have been observed to enter these excavation tunnels, and larger predators (herons, storks, skunks and weasels, for instance) may wait by a fresh opening for the digger to return with its next load of soil.