Meaning of Subtle: (especially of a change or      distinction) so delicate or precise as to be difficult to analyse or      describe. making use of clever and      indirect methods to achieve something. (of a mixture or effect)      delicately complex and understated.The Serpent in the book of Genesis represent the enemy(Devil).Most of us thought we have known everything about the enemy.This is one of the issue with our Christian ASSUMPTION.Little did we know that the devil works in the way we least expected. The ways we do not really see how shrewd he can be.The enemy has many times capitalized this. I have no doubt this is what Apostle Paul was saying:2 Corinthians So we look not at the things which are seen, but at the things which are unseen; for the things which are visible are temporal [just brief and fleeting], but the things which are invisible are everlasting and imperishable.Jesus Christ did not just send the Holy Spirit to us because it is the normal ritual. He did because many of us cannot survive the woes the enemy will play on us.Don't forget the Enemy is: Imposter -Matthew But while everyone was sleeping, his enemy came. The enemy planted weeds among the wheat and then went away. Persistent -Ephesians In addition to all of these, hold up the shield of faith to stop the fiery arrows of the devil. Deceiver -John You are of your father the devil, and it is your will to practice the desires [which are characteristic] of your father. He was a murderer from the beginning, and does not stand in the truth because there is no truth in him. When he lies, he speaks what it natural to him, for he is a liar and the father of lies and half-truths. Manipulator - Seducer -1 Timothy Now the Spirit speaketh expressly that in the latter times some shall depart from the faith, giving heed to seducing spirits and doctrines of devils, Cunning - Thief -John The thief comes only in order to steal and kill and destroy. I came that they may have and enjoy life, and have it in abundance [to the full, till it overflows].