Rasoul's head came rolling down while his boy was still rooted to the same spot. It happened quickly and unexpectedly, so it took the audience a few seconds to register what had happened. Once they saw Rasoul's head rolling on the flow, their cheers and how shot up to a new height.
They all celebrated the berserker for making their wishes come true. From the start, they all wanted Rasoul dead and now that their wish came true, the only thing left for them is their cheers and happiness.
Karsha looked at Rasoul's head rolling on the floor with a slight smug. He accomplished what he wanted - using Rasoul as a stepping stone. But somehow, he felt the battle hadn't ended so without a second thought, he stepped on the head rolling on the floor. And like he expected, the head started dispersing instead of splashing goo everywhere.