irb --> h = Hash.new({})
    ==> {}

irb --> h[:one] = 1
    ==> 1

irb --> h
    ==> {:one=>1}

irb --> h[:two][1] = "one"
    ==> "one"

irb --> h
    ==> {:one=>1}

irb --> h[:three] = 3
    ==> 3

irb --> h
    ==> {:one=>1, :three=>3}