We need to puts animals into the num_pets array which currently does not exist.  You need to change the initialize method to create an empty num_pets hash (note when you instantiate new client you now only have 3 arguments). 

      class Client 
 	attr_accessor :name, :num_children, :age, :num_pets
 	def initialize (name, num_children, age)
 		@name = name
 		@num_children = num_children.to_i
 		@age = age
 		@num_pets = num_pets
 	end
 
      def to_s
         puts "#{@name}"
      end
 end