US Patent 7172505 Slot machine bonus initiated by plural qualifications

A multi-stage method qualifies a player for a bonus game. If two stages are used, the first has the player aligning a combination including at least one trigger symbol. The second stage uses the trigger symbols, reel symbols, other secondary mathematically related elements, or elements associated therewith, to qualify the player for the bonus game. The player interacts during the qualification process by providing input to the second stage.