They can smell a change in the chemicals their body makes.
No words can "actually" answer this question. Your going to have to find out yourself or ASK MILLY!!!
Sim Hae-In was born in 1987.
Lee San-hae died in 1609.
Song Hae-seong was born in 1964.
Yi Hae-won was born in 1919.
Jung Ji-Hae was born in 1985.
Chung Hae-Won was born in 1958.
Hae Jong Kim was born in 1935.
Park Hae-Jung was born in 1972.
Lee San-hae was born in 1539.
Min Hae-Kyung was born in 1962.
Kwon Geun-Hae was born in 1987.