The Gramda she tried to learn idioms to become a "true American" she constantly brings birds into the letter with oskar and that could relate to the idiom two love birds between her and her husband.
When one door closes another one opens.
" It is! I never heard from her again! Oh, well ! So many people enter and leave your life! Hundreds of thousands of people! You have to keep the door open so they can come in! But it also means you have to let them go!"
Oskar hasn't closed the door on his father. He is examining the door and its key.