$dad=Sr
$dad=Sr -> $son=Jr
$dad=Newt; Sr -> $son=Jr
Sr no longer referenced, but not destroyed yet.
DESTROYing dad: Sr
$dad=Newt -> $son=Jr; (Sr destroyed)
Young never really referenced, but not destroyed yet.
$dad=Newt -> Young; $son=Jr
DESTROYing son: Young
DESTROYing dad: Newt
$dad=Fin; $son=Jr (Newt -> Young destroyed)
Rest to be destroyed next.
DESTROYing son: Jr
DESTROYing dad: Fin
Everything destroyed above.