Sensual perception of remote objects by processing of radiative stimuli is a capability widely encountered in animals. Humans perceive only passively, that is, see and hear objects that either radiate themselves or scatter and retransmit radiation from an external source. Some animals can locate objects actively as well, using optical or acoustical radiation they generate on purpose. Several species of fish literally carry lanterns. Horses and elephants are known to utilize active acoustic means for orientation in complete darkness. Bats use it to locate and catch prey.