The extinguishment of the candle flame in the well-known candle-and-cylinder experiment has been erroneously viewed as caused by the complete consumption of oxygen, for many reasons. To address this misconception scientifically, a series of experiments are carried out to illustrate the phenomenon from a new point of view. Limewater [Ca(OH)[subscript 2]] placed at different heights in a container was used to qualitatively describe the distribution of CO[subscript 2] in an enclosed cylinder with one or two burning candles. Temperature sensors, CO[subscript 2] sensors, and oxygen (O[subscript 2]) sensors were employed to visually and quantitatively compare the content of CO[subscript 2] at different heights within the container. The resulting temperature curves show that the heat from combustion rose first and then descended soon afterward. Chemical and sensor detection of CO[subscript 2] in the highest two quadrants of the container indicated that the hot CO[subscript 2] gas rose initially and accumulated there in the highest part of the container. Then, the hot CO[subscript 2] gas descended gradually and created a CO[subscript 2] atmosphere surrounding the flame. As a result, the flame was extinguished by the buildup of CO[subscript 2] and depletion of oxygen in the gas in the vicinity of the flame. The change of oxygen concentration showed that there was a mixing process between the remaining air and the hot CO[subscript 2]. These results indicate that the extinguishment of the flame does not mean that the oxygen in the container was completely consumed. Knowing this helps students understand that the density of CO[subscript 2] depends on its temperature.