Summary: We propose a reversible and local rule that allows large-scale objects called ‘strings’ to move with adjustable speed and energy in a three- dimensional space. We show that the motion of these strings is governed by discrete Hamiltonian equations and mediated by one longitudinal and two transverse sound waves that propagate along the string. This rule is a first attempt to model a solid body with a cellular automaton. It also provides interesting possibilities for simulating new physical situations.