In plain words
When this Bhīṣma, an elder, the grandsire, a jñānī, is giving his message, for a woman, an ordinary woman, to laugh like this, is that not an insult? Bhīma grew angry that this woman, who should have shown humility and obedience, had laughed. He rolled his eyes. Arjuna's eyes turned red. Dharmaja bowed his head. Nakula and Sahadeva were grieved. They went on lamenting to one another that the whole honour and good name of the Pāṇḍavas was being brought to disgrace by a thing like this. Bhīṣma understood it well: 'Dharmaja! Draupadī has a very great Buddhi. There is no pativratā in this world to surpass her. None is to be found. She is a woman of great virtue. She has virtues that no one else in the world has. She does nothing without a reason. So there is a reason for this laughter. I shall prove that reason now; watch,' he said, and called, 'Mother! Draupadī, come here.' 'Explain clearly the reason for your laughter, and teach it so that your husbands understand,' he said. 'Grandsire! The fault is mine. But what is the point of teaching the Pāṇḍavas, who are devoted to Satya and Dharma, the lessons that should be taught to the Kauravas, who behaved with injustice, wrongdoing, misconduct and Asatya? Though you are the commander of the Kauravas' army, you are teaching the Pāṇḍavas what you should be teaching the Kauravas. The Pāṇḍavas have never practised Adharma. They have never entered into wrongdoing. They are ever vowed to Satya. For people like these, who live by Dharma, your teaching is simply going to waste; that is what grieved me,' she said. All your teachings are urgently needed by the wicked and the evil-minded. Then Bhīṣma said: 'Draupadī! I was on the Kauravas' side. All my food was food the Kauravas gave me. I have eaten their salt and their tamarind. So, by eating food bound up with their injustice, wrongdoing, misconduct and Asatya, all my blood turned into injustice and wrongdoing. Through the arrows your husband Arjuna shot, all that tainted blood has flowed out. The Dharma that lay at the very bottom of it is now coming up. All this time this bad blood has covered my Dharma, my vows, my sense of justice. So now all that tainted blood is gone. Justice and Dharma, hidden at the bottom, are now welling up, Draupadī!' he said. So consider how great the power of food is. Through Draupadī's laughter this truth came out.