Whats the difference between monster.print_score and puts monster.print_score?

This has to do with how the print_scoreboard method was defined within the Monster class.

  def print_scoreboard
    puts "------------------------------"
    puts "#{name} scoreboard"
    puts "------------------------------"
    puts "- Screams: #{actions[:screams]}"
    puts "- Scares: #{actions[:scares]}"
    puts "- Runs: #{actions[:runs]}"
    puts "- Hides: #{actions[:hides]}"
    puts "------------------------------"
  end

You see, there're multiple lines of puts statements in the print_scoreboard method body, the job of the puts statement is to output the result to your screen; thus by simply calling the monster.print_scoreboard, the result will be outputted to the screen.

If, however, the print_scoreboard was defined in a different fashion, say, sth like the following.

def print_scoreboard
  return "some value"
end

It uses return statement instead of the puts, in this case, by calling monster.print_scoreboard, nothing will be printed, as return statement does not output the result on screen; now it's necessary to pass the method call to puts as argument -- puts monster.print_scoreboard. Does that make sense?