When a lion attacks his prey he does not first roar and give his presence away. He stalks his prey because he is hungry and in need of food.  
   Many times the female lions in the pride will work together to bring down their prey and then will allow the male that protects their pride to eat first. The pride of female lions move in silence trying to stalk their prey when they are the most defenseless. They choose the unwatched youngster or the old and weak for there victims.

 Satan is the same way. He does not alert the child of God first to let them know that he is up to no good. He watches for the times that a Christian is less defensive so the Christian will not have time to prepare and put his armor on.  

A Christian must at all times be prepared by keeping his or her armor on, so the enemy will not have a chance to destroy them.

 After Satan leads a person into sin he then roars because the child of God already knows that he has been deceived.