I know AHBD will see this, but I will flag it for her, as she has done years of breeding.
Have your other eggs already hatched out? How long has this egg been like this?
You can never tell for sure but if it was already actively attempting a bite then it would seem to be viable. Has it hatched yet , if so is the yolk sac still attached ? I had twins hatch before and they came out of opposite ends of the egg so that's what came to my mind when I saw this. I actually took a pic of it :