You control a ball by swiping left or right to collide with other balls sharing the same number. Colliding doubles the ball's value (e.g., two "2" balls merge into a "4").
Hitting static spikes or moving thorn traps does not kill you instantly, but it violently divides or reduces your ball's current number. Rebuilding a massive number after hitting a spike is incredibly difficult in later stages.
You must avoid falling off the rail or hitting "thorns" (obstacles) that decrease your number or reset your run.