Reincarnated As A Mosquito - Chapter 27:

... the waggon on.

[In short, if you kill a normal-tier beast, you will obtain this thing in place of their heart.]

Ok, and I need three of those things. Not a problem," he said in a serious tone before Ben activated his new 'Blood Vision' skill to look for prey. After the upgrade, not only could he see quite far with that skill, but he was even able to determine targets health and strength depending on the intensity of the blood aura coming from them.

"Found one!" Ben claime ...