Some kinds of animal movement,
such as the slow progress of a limpet as it creeps across
rocks, are so slow
that they are almost imperceptible. Others, such as the attacking dive of a
peregrine falcon or the leap of a flea, are so fast that they are difficult or
even impossible to follow. Many single-celled organisms can move, but in
absolute terms, animals are by far the fastest-moving living things on earth.