Waste
The foot couldn't measure differences in power from the exchange, but the roar overcame that barrier, conveying the massive gap from Khan. The two weren't even comparable.
Khan's roar didn't carry any specific meaning. He had forwarded his overbearing and unreasonable intensity, declaring who was in charge of the situation, and the foot understood its place.
The energy inside the foot slowly dispersed, abandoning its condensed state and leaking into the hall. Part of it even permeated Khan's skin, but his flesh didn't react. No absorption happened.
The previous tests had forced Khan to consider that eventuality, so the result didn't surprise him. It made sense that his body couldn't absorb anything from the Nak since his transformation was complete. That further reassured him but also killed any hope of obtaining immediate improvements.