Natyashastra
हसितरुदितादिसंभ्रमभयश्रमव्याधिपीडितार्थेषु । नानाभावोपगतं कार्यमुरो नाट्ययोगेषु ॥ २३१॥
The breast is recognized as Prakampita (shaking) in situations of laughter, weeping, confusion, fear, fatigue, and ailments. It is also associated with various emotional states in dramatic performances.
english translation
hasitaruditAdisaMbhramabhayazramavyAdhipIDitArtheSu । nAnAbhAvopagataM kAryamuro nATyayogeSu ॥ 231॥
hk transliteration by Sanscript