In plain words
She is very pure. There is no room to find fault with her. She does not laugh without a reason. I am the reason." Saying this, he called her near: "Draupadī, come." "Mother! Tell us why you laughed. Many will come to know the truth." Then Draupadī said: "Grandsire! We always give honour to your word. We are dedicating our very lives to Satya. In such a matter it is not possible for me to laugh in jest. But from the very beginning you stayed on the side of the Kauravas and stood as commander of the Kaurava army. You brought up the Kauravas from their childhood. Why could you not have told these dharmas to the Kauravas? To my husbands, who are Satya and Dharma embodied, you need not tell the dharmas. They are men who know Satya and Dharma. But why did you not give these teachings to the Kauravas, who did not know Satya and Dharma? That is why I laughed. You did not teach those who should be taught. You are teaching those who do not need it. This is not right for elders like you." She spoke the truth. Then Bhīṣma saw the truth and spoke. "Yes, the fault is mine. From the beginning I went on eating the food of the Kauravas. I went on living my life in the midst of the Kauravas. Because I ate that sinful food, the principles of Dharma in me sank to the very bottom. My sinful feelings kept rising to the top. Today, through the arrows your husband shot, all the blood on top has drained away. The bad blood is gone. The blood of evil intellect and evil feeling has drained away. Now steady, pure blood is welling up in me. That is why I am teaching. The root cause of my not teaching this Dharma all this time is the food of the sinful Kauravas: it created this kind of fault." The faults of the food we eat are many. When we eat sinful food, sinful feelings alone come out of us. Bhīṣma was a great jñānī. But what was the reason such evil feelings came to him? He ate wealth gained by sin. As the food is, so the head becomes. He owned that his fault was of this kind. There was no fault at all in Draupadī's laughing. She laughed because I was giving teachings.
Then the ṛṣis and the kings recognised, in that day, that there could be so much fault in food and drink of this kind.