心如西瓜自然甜心如柠檬自然酸
[xīn rú xī guā zì rán tián xīn rú níng méng zì rán suān]
This phrase means 'A heart as sweet as watermelon naturally sweet, a heart as sour as lemon naturally sour', symbolizing that emotions come from within and manifest naturally; sweetness or bitterness depends on one's true nature.