A slot machine conducts a wagering game in which a plurality of arrays of symbols are successively displayed. Each array may, for example, result from a free spin of a plurality of symbol-bearing reels during a bonus feature. In each free spin, the reels are rotated and stopped to place the symbols on the reels in visual association with a display area. In response to a random event, at least one symbol may change its function and maintain that function for a plurality of the successive free spins. For example, the symbol may become a wild symbol or a scatter pay symbol. Payouts for the free spins are awarded according to a pay table.