User blog comment:IamJakuhoRaikoben/Chapter 412: Dance Unto Ishgar, Review./@comment-9595671-20141208153136/@comment-9595671-20141208164116

Yeah, I have some ideas already, for one I did see Ingeel bleeding in this chapter, and I don't think a young child knows how to check for a pulse, much less a dragon's pulse. They also probably don't know how much bleeding (for a dragon or overall) is actually lethal so they could have just stopped moving to make it look more convincing.

Considering how long it takes for a body to turn into bones its quite possible they uses that to fake being dead. (This helps Sting bathe in his dad's blood, and Skiadrum could have easily faked illness since Rogue likely doesn't know about dragon diseases.)

And if you wonder how'd they get inside their sons' in that case, they likely had to do it when they wouldn't see them, when they were asleep. If you recall all of the other Slayers' dragons vanished without explanation, its likely they all did it while they were sleeping as that's the only time they wouldn't have noticed.