"and Spread" is an add-on to another call; the action depends
on who performed the call and the formation at the end of that call.

Case 1:

If specific dancers did the call (for example, Heads Star Thru) then
then that couple will, after completing the call, spread apart and the
inactive couple will move in between them to form a line.

Case 2:

If the Anything call ends in tandem couples (one couple behind
the other) the leading couple will spread apart and the trailing couple
will step forward between them to make a line

Case 3:

If the Anything call ends in a line or an ocean wave the dancers
who would have become centers in the new formation will slide apart to
become the ends and the dancers who would have been ends will slide
together to become the centers of the new formation.