Viyahapannatti 10.3.483

10.3.483

āsassa ṇaṃ bhaṃte! dhāvamāṇassa kiṃ khu-khu tti kareti?
goyamā! āsassa ṇaṃ dhāvamāṇassa hiyayassa ya jagassa ya aṃtarā ettha ṇaṃ kakkaḍae nāmaṃ vāe saṃmucchai, jeṇaṃ āsassa dhāvamāṇassa khu-khu tti kareti|

"Venerable Sir, why does a running horse make the sound 'khu-khu'?"
"Gautama, between the heart and the liver of a running horse, there an air called karkaṭaka forms, because of which a running horse makes the sound 'khu-khu'."