Observe, choose, check
In brief
A screen for the cannon
A screen for the cannon
In this teaching diagram, the red cannon on B3 is targeting a black piece on B8. A single screening piece occupies B5, and the other intersections between B3 and B8 are empty: the capture is possible.
Why can the cannon capture?
Show the answer
The cannon captures on B8 by jumping over the single screen on B5. With no screen, or with two screens, this capture would be illegal.