At this stage of development, a person's discriminative intelligence, which is developed at the spiritual stage of tortoise gets refined. He learns to differentiate between purity and impurity the way a duck differentiates between water from silt.

If we want to understand the sense of discrimination, we need to know the behaviour of a duck. It will take in everything through its mouth, but it will not take in the dirt. It will take in only water and worms. It has got discrimination. The discrimination of a Swan is superfine, this is gross. Milk can't be differentiated, without a meter. It is in Zoology textbooks. The duck won't swallow dirt. It will only take in worms and water.

The tortoise in the previous cell withdraws with sense of discrimination, due to the pratikulyasya varjanam. Here it is discriminative intelligence of superior variety. Here it knows what it wants and what it doesn't whereas the tortoise has withdrawn limbs out of fear, with any kind of sound. Viveka is getting refined is the point to note here.