With a psychotic grin at the agents pain he released him, the carved message ceasing, leaning back he surveyed the blood and smirked. The blood had seeped through in a distorted shape of the words he'd carved. Standing Loki patted Coulson on the shoulder, condescending till the very end and sauntered over to the door and turned with one last barb.
"Be a good little doggy and don't forget to tell your master~" Then he turned and left, leaving the paralysis still in place.
A harsh whispered filtered through the air, right next to Coulson's ear, "If you value your tongue, you'll hold it when you address me, else i'll cut it out and keep it in a jar~"
As soon as they'd appeared the voice and presence disappeared, releasing the spell with it.