What's the recommended Ruby way to do abstract classes and abstract methods?

Related : what's the Ruby way for interfaces?

While Googling for it, I was thinking about what abstracts and
interfaces are used for in Java and PHP5 ... and it came down to
stopping with errors if a certain method was NOT implemented.

So... is that kind of thing just not the Ruby Way?  (To give you
errors for not doing something.)

Would I just do workarounds to say:

class AbstractSomething
  def method
    puts "error - abstract!"
  end
end

Or does Ruby have a whole different approach to this that I missed somewhere?