What he didn't realize was that he and his sisters dad wasn't actually their biological
father.His girlfriends dad was.
Now that his girlfriend was 50% dragoness it meant his parents
were both 100% dragons.
The second he hit save the program recalculated all the numbers,took into
account the environmental temperatures at the time their mother laid her dragons eggs.
It was the kind of temperature that causes the reptillian eggs to switch genders
from male >> female through the whole clutch.
Her girlfriends first indication of this was the surprised bellow as the
dragoness sprawled on all fours trying to tear away the constricting human
clothes with her new acquired pointy teeth whacked over the computer with her
spiky tail.
There was the sound of crashing smashing hardware...