At 8:06 that was not sweat that flew off his face when The Man That Ate Popeye struck him, but was cerebrospinal fluid that flew out his ear. CSF is a clear fluid that surrounds the brain and spinal cord. It cushions the brain and spinal cord from injury and also serves as a nutrient delivery and waste removal system for the brain.
In other words Sergei literally had the schit knocked out of him.