Reason behind Draupadi collecting blood of Yudhishthira in water

Question

In Mahabharata, king Virata, out of anger, strikes Yudhishthira's face. Then Draupadi collects the blood due to that act by Virata.

"Vaisampayana continued, 'Saying this, the king inflamed with anger forcibly struck Yudhishthira in the face with a dice, and reproached him angrily, saying, 'Let it not occur again! And having been violently struck, blood began to flow from his nose. But the son of Pritha held it in his hands before it fell on the ground. And the virtuous Yudhishthira then glanced at Draupadi who was standing by his side. Ever obedient to the wishes of her lord, the faultless Draupadi, understanding his meaning, and bringing a golden vessel filled with water, received the blood that flowed from his nose.

[Section 67, Go-harana Parva, Virata Parva, The Mahabharata]

Is there any hidden reason behind collecting blood in water? Do scriptures say that blood should be collected in water or blood should not touch the ground?

Answer 1

They didn't want the blood to touch the ground because they wanted to hide this incident from Arjuna (Vrihannala) to save Virata and his kingdom.

From the same chapter that you used in question,

Let Uttara enter alone; Vrihannala must not come in. Such is the vow of that hero of mighty arms that whoever causeth a wound on my person or sheddeth my blood except in battle, shall not live. Inflamed with rage he will never bear patiently to see me bleeding, but will slay Virata even now with his counsellors and troops and steeds.'"

In next chapter, we find that Vrihannala entered when bleeding stopped and they already collected blood in vessel so there were no signs of blood on ground.