We need to be as alert as animals that there are things be wary about - false teachers. Over and over throughout the New Testament, we are warned about wolves in sheep's clothing. They look like bring truth, but their fruit is evil. It:
Comes from Within themselves and points to themselves
They have gone the way of Cain
They run greedily in the error of Balaam
They are like those who perished in Korah's Rebellion
Their characteristics include grumbling, finding fault, speaking arrogantly