gistfile1.txt

class Thing
  def say_hi
    puts "Hi"
  end
end


thing = Thing.new
thing.say_hi
# "Hi"

gistfile2.txt

class Thing
  
  private

  def say_hi
    puts "Hi"
  end
end

thing = Thing.new
thing.say_hi
NoMethodError: private method `say_hi' called for #<Thing:0x007fcf9d699fa0>
	from (irb):11
	from /Users/njero/.rbenv/versions/2.2.1/bin/irb:11:in `<main>'

gistfile3.txt

class Thing

  def say_something
    say_hi
  end
  
  private

  def say_hi
    puts "Hi"
  end
end

thing = Thing.new
thing.say_something
# Hi