Ruby operator method calls vs. normal method calls

I'm wondering why calls to operator methods don't require a dot? Or rather, why can't normal methods be called without a dot?

Example

class Foo
  def +(object)
    puts "this will work"
  end
  def plus(object)
    puts "this won't"
  end
end 
f = Foo.new
f + "anything" # "this will work"
f plus "anything" # NoMethodError: undefined method `plus' for main:Object