  We study the interaction of both dense and sparse multi-armed spirals in
bistable media modeled by equations of FitzHugh-Nagumo type. Dense 1-armed
spiral is characterized by its fixed tip. For dense multi-armed spirals, when
the initial distance between tips is less than a critical value, the arms
collide, connect and disconnect continuously as the spirals rotate. The
continuous reconstruction between the front and the back drives the tips to
corotate along a rough circle and to meander zigzaggedly. The rotation
frequency of tip, the frequency of zigzagged displacement, the frequency of
spiral, the oscillation frequency of media, and the number of arms satisfy
certain relations as long as the control parameters of the model are fixed.
When the initial distance between tips is larger than the critical value, the
behaviors of individual arms within either dense or sparse multi-armed spirals
are identical to that of corresponding 1-armed spirals.
