The cost were given before the serpent ever entered the picture. This wasn't an error of wonderment because the snake was new; they named the animals! No, they trusted this created thing more than God...they didn't reason or use wisdom to ask "why is the snake suddenly talking in our language? Did it speak when we named it? Did anything else suddenly develop “a voice”?" Clearly the ability to reason and discern subtle differences between truth and error was resident! Look how many insects and SNAKES look alike! Just as now, God allowed them to make an educated and informed choice about life. Just like today, it is easier to believe what's in front of us than to take a moment and seek a higher truth.