Also, this might be interesting for you guys - here is an answer to a good question about Flashcast:
Q: Why did professors think Kiel managed to Flashcast and Deora thought Kiel's casting speed was very high? Couldn't he have concealed his weaving and then stopped concealing it when it formed causing an illusion that his weaving was quick?
A: In normal casting the mage weaves a spell pattern and when finished that spell pattern creates a reality altering effect. Flashcast is different, it's like reverse casting - the reality altering effect happens first and forces its spell pattern to form.
In mana sense of others they would see mana congregating and forming the spell pattern almost instantaneously and mistake it as a person having an extremely fast casting speed.
However, more experienced spectators would notice that the reality altering effect appeared before the spell pattern and recognize it as Flashcast.
If Kiel had concealed the spell very well, spectators would feel an area with little or no mana, and then when he stopped concealing it, it would feel as if the spell along with a bunch of mana teleported there, popping out of nowhere. Like they blinked and missed what happened.
It doesn't look or feel the same.