Could somebody please explain why the variable named foo remains true in the code below, even though it's set to false when the method is called? And why the symbol version behaves as expected?

def test(options = {})
  foo = options[:foo] || true
  bar = options[:bar] || :true
  puts "foo is #{foo}, bar is #{bar}"
end

>> test(:foo => false, :bar => :false)
foo is true, bar is false

I've only tried this using Ruby 1.8.7.