Thank you, thank you!!! I don't know if you recall saying, like early this year in your IJ, that you hadn't read a fic in which Harry is bitten by Nagini and then has to be saved by Snape in a fuck-or-die scenario? Well, I played with that idea a bit to make it one of Nagini's offspring, but I really hope you like the results -- definitely began as a seed from your comment!
I'm so glad you liked the twist in the potion's composition -- and yes, Snape definitely panics -- fear of happiness, poor thing.