Lines 89 -120 would look nicer like this: 

            puts "Choose a client #{shelter.clients.keys.join(',')} "
        # puts "Which client wants to adopt? "
        adopting_client = gets.chomp

        puts "___________________________________________________"
        puts "Which animal do you want to adopt #{shelter.animals.keys.join(',')}"
        adoptionAnimal = gets.chomp

        animal = shelter.animals[adoptionAnimal]
        shelter.animals.delete(adoptionAnimal)
        puts "#{adopting_client} has adopted #{adoptionAnimal}! Thanks #{adopting_client}!"
        puts "___________________________________________________"
        
        shelter.clients[adopting_client].pets[adoptionAnimal] = animal