Halliday & Matthiessen (1999: 118):
There is no sharp line between a figure and a sequence of figures: a quantum of experience is not defined before it is construed, and the grammar rather sets up a cline from sequence to simple figure. […] For example:
1 sequence of 2 figures: Tarzan pulled the rope; so it broke.
Tarzan made the rope break (by pulling it).
Tarzan broke the rope.
1 figure: The rope broke.