Oni sucks more blood than he needs to when he is almost full

Yords

For example, when you have 99% of your blood fury, you need only one blood orb to finish it off. However, when you go to suck up just one in a pool of 12 orbs, you would actually take about 6 extra orbs. This scales up and can cost you a lot of orbs you would have gotten otherwise.

To recreate: Literally, play Oni. There are no specifics to this.