The Pater would not find the sweet smell of sweat and tears it would usually find on frequent lot who would summon it.  Nergal was from a dark world where rituals to the dark gods of his realm were common.  In fact the creature if so attuned would likely be able to recognize the dark magical pacts infused into the body of the one who summoned it.  Nergal was calm as the creature stood before him, his visor giving him a visual of the creature.  The visor wasn't necessary as the darkness flowing through his own body was warning him of the creatures presence, sensing its vileness. 

It was time to finish his work though and Nergal began to speak to the creature.  "I have summoned you Magna Pater.  My Company wishes to examine you and preferably alive.  I know creatures like you have an intelligence that most mortals do not understand, so this is a choice between coming with me alive or me having to bring some samples back the hard way."

He raises his sword the blood drinker up now in a normal stance with his feet spread slightly apart with both hands holding the sword slightly to his right side.  The blade is tilted back with its tip barely pointed to the ground.  His gauntlet which injects a tube into his arm lets the valve open to allow the blood to seep out through the delivery system to the blade.  The blood slides into the grooves on its side.   He is ready for a melee attack of any sorts but he knows that the Pater is likely smarter than it looks.

Using an unholy rune, a blood rune, and a dark rune from his body the blood inscribed tetrahedron glows for one brief moment and then suddenly out of its edges bones raise up and try to snap shut on the creature to form a giant bone prison for it.  The bone bars resemble fingers almost clasping it to hold it down.  The blood that was once there seems to have now been used up by whatever spell was invoked onto it.  

Having expended a shadow rune before and now three for this spell, two death runes appear onto his weapon above the others.  The dark rune he used before is half charged with a blood, unholy, and dark rune exhausted and beginning to charge again.  He still has a blood and an unholy rune to use on his body with his weapon still holding two blood and two dark.