The Pokédex provides additional biological info about the Jigglypuff species: After it mesmerizes its foe with its large, round eyes, it sings its lullaby until the foe sleeps, and does not stop to breathe until the foe is fully asleep; it can perform longer with its single breath if it inflates its body with air beforehand. Its vocal cords can freely adjust the wavelength of its voice, and it sings at precisely the right wavelength to make its foes most drowsy. The sound waves of its singing voice match the brain waves of someone in a deep sleep. Nothing can avoid falling asleep after hearing a Jigglypuff's song, but some are more naturally resistant to the effects than others and take much longer to sleep. This effectively endangers a singing Jigglypuff's life because it cannot breathe.