if, after a column has fallen, there are three or more of the same symbols connected in a straight line horizontally, vertically, or diagonally, those symbols disappear. the pile of columns then settles under gravity. if this causes three or more other symbols to become aligned, they also disappear and the pile settles again. this process repeats as many times as necessary. it is not uncommon for this to happen three or four times in a row - it often happens by accident when the well is becoming crowded. if the well fills beyond the top of the screen, the game ends.