The fact that every time Deviu bit down on to small enough vine that it shriveled up and cut itself off was amazing. This meant that the beast controlling these thorny vines was definitely feeling the dangers that came with Devi's chilling bites.
The further fact that Devi gained some energies from this was even more important. Especially since Devi was stocking a ton of soul and death energy to be able to grow. He had clearly felt Clark's intentions and desires to grow stronger.
The supportive feelings only pushed Devi to begin preparing even more. That was why he showed a lot of emotion upon realizing that along their way within this broken dungeon, he could gain a lot. Especially with the fact that there were many linked beasts that had a myriad of unique energies that could be converted in to food for him.
