The author wants you to see that this rodent was born into a life of hardships and never got to experience a normal life without danger.
a cotton ball is a lifeless ball of fluff, which is how the rodent is treated in this giant city. It is kicked and run over as if it were an object, where the people don't consider the feelings of the rodent.
the tail being described as a toothpick I think represents the life of the rodent, unmoving and painful. The rodent's life will never change, it will keep on experiencing the pain life gives it.
The pigs gain the rights to the cow's milk by telling the other animals that it was for the "benefit of the farm". ... This event suggest about power hierarchy on the farm that it belongs to the pings and not to all the animals.
