Drag back the sling, release to fire a parabolic shot, and knock out every target on the level with the fewest stones.
A sling sits on the lower-left of the screen. Touch anywhere on the field and drag: the stone is pulled back from the sling, and the further you pull (pointing away from where you want it to fly), the harder the throw. A dotted arc previews about 1.5 seconds of flight, including one bounce. Release to fire. Each balloon you pop is worth 100. Pop every balloon on the level to advance: you get +200 for every unused stone plus 50 × the level number. Levels 1–8 give 3 to 6 stones; from level 9 you lose one stone every two levels (5 at levels 9–10, down to 1 at levels 17–18) while there are still 8 balloons, so every run ends. Run out of stones with balloons still floating and the run is over.
Read the arc before releasing, but know its limits. The dotted preview follows the stone for about 1.5 seconds and one bounce, and it ignores balloons: after each pop the stone keeps flying at 78% of its speed, so anything it reaches after the first hit lands short of the dots. Adjust the pull until the arc crosses your first balloon, then let go — a two-second pause to aim beats a fast miss.
Pull at an angle that exploits gravity. A long, flat pull launches the stone fast and low, which suits the nearest balloons. For balloons at the back of the screen, pull further down so the stone climbs high; it then drops onto the far balloons instead of sailing over them.
Line balloons up on one arc. A well-aimed stone can pop several in a row, and an unused stone is worth +200 — twice a single pop — so look for clusters before every shot. From level 9 the stones shrink by one every two levels while eight balloons remain, so multi-pops are what carry a run past the low teens.
Don't ignore the floor. The stone bounces once with reduced energy and can roll along the ground, so a low skipping shot can still sweep up balloons floating just above the grass.