Anger is the state of the mind triggered by physiological and emotional response that can range from mild irritation to intense rage. People get angry when they experience a perceived threat, injustice, or frustration. It is always suggested to avoid confronting an angry person, but the question is how to identify, if the person is in anger or not. There could be many sign of an angry person but if the person does now vent out his frustration it get difficult to know if the person is angry or not. Sanskrit identified a good way to notice anger in a person, it says ;
अभ्यासाद्धार्यते विद्या कुलं शीलेन धार्यते|
गुणेन ज्ञायते त्वार्यः कोपो नेत्रेण गम्यते||
Abhyaasaaddharyate vidyaa kulam sheelena dhaaryate.
Gunena gyaayate tvaaryah kopo netrena gamyate.
Abhyaasaaddharyate = abhyaasaat + dhaaryate.
Abhyaasaat = through regular practice.
Dhaaryate = maintained , retained .
Vidyaa = knowledge, learning.
Kulam = a family dynasty.
Sheelena = by the moral conduct, integrity.
Gunena = virtues merit.
Gyaayate = known, recognised.
Tvaaryah = tu + aaryah.
Tu = and, but.
Aaryh = a noble person,
Kopo = rage, anger.
Netrena = by the eyes.
Gamyate = explained, demonstrated.
i.e. Knowledge and learning is retained through regular practice and the fame of a family dynasty is maintained through the integrity and good moral conduct of its members. A noble and righteous person can be identified by his virtues and an angry person can be identified through his (red) eyes.
It says that, like practice helps us to retained the knowledge , and moral conduct helps us to identify the family legacy, likewise, anger can be identified through redness in eyes.
The redness in eyes on getting angry is a natural process. Infact I learned the same few days ago in my school. It states; When someone is angry, the body's sympathetic nervous system can be activated, leading to increased blood flow to various parts of the body, including the face and eyes. The white part of the eye, the sclera, can appear red due to increased blood flow to the conjunctiva, the thin layer covering the sclera.