He said to the fire god, "I will now send you to your maker. Isn't that great?"
He said that, but he still didn't release the fire god. What he did was to mark the fire god. Then he pressed his hand on top of the fire god's head to crush it.
The fire god can avoid this kind of physical attack by turning into a nest of fire serpents. But Loki had convinced it not to try to avoid the danger.
His words were very convincing, so the fire god lay there as he crushed its head. But even this wasn't enough to kill the fire god.
The support of the world meant that it could continue to live without its head. It can even heal the injury to its head if Loki gives it the chance to.
But Loki didn't give it the chance to recover. He also shattered the fire god's mind. Then he got to work cutting the fire god to pieces.
