"That's..."
"Orochimaru's blood. I collected it casually before, and now it's time to put the waste to good use."
They had to admit that scavenging was something deeply ingrained in the memory of the human race. After seeing something that seemed worthwhile, who cared who had thrown it away or whether it would be useful later? The important thing was to collect it first. Sooner or later, it would come in handy... Orochimaru's blood was one such thing. It might be useful, or it might not, but there was no doubt that it was rare. Since it was rare, it had to be collected.
Such things were even more common among ninja. Of course, what one saw most often was not the collection of blood, but retrieving an enemy's corpse after killing them for intelligence analysis and other research. This shameless tradition of stealing odds and ends from other people's bodies probably traced back to the time Madara Uchiha took a bite out of Hashirama Senju.
Clearly, no matter how domineering Madara Uchiha had always appeared, he was not a particular man in reality. If he wanted to steal—or bite—a man, he simply did it.
"Using Orochimaru's blood for summoning? In theory, it can indeed be done. After all, this blood contains the corresponding contract link. However... whether the Summoning Beast will respond to chakra belonging to someone other than Orochimaru is another matter," Kushina said. She wisely refrained from investigating how Yuhara had obtained Orochimaru's blood.
Using Orochimaru's blood to form hand seals and summon would certainly establish contact with the Summoning Beasts of Ryūchi Cave. The problem was whether the Summoning Beast would respond to this summoning, and it could not choose whether to respond. After all, it—or they—could sense that the chakra summoning Manda did not belong