It can't be an animal or bird, as animals do not knock on doors.
It can't be a human, because the human will shout "hello, pse open
your window, I want to come in", if u keep ignoring his
knocking.
Luckily u never left your windows open, or the ghost will just drop
in without having to knock.
Previously there was a news in malaysia about a group of workers
who saw a old male ghost enter from one window and left through
another window in their living room at midnight.
