The obvious answer is the return of the Master because the drumming he heard is four knocks, but David Tennant and Julie Gardner said on the Planet of the Dead commentary is not what we think it is, Julie also said when we figure it out it will break our hearts.
Just as the doctor believes he's safe at the end of 'The End of Time', he hears four knocks. Wilfred Mott, Donna's grandfather, is stuck in a booth that's about to be flooded with lethal radiation. It is he who knocks four times, and the Doctor, being who he has, entered the booth next to it to allow Wilfred to leave. The Doctor receives the fatal dose of radiation, which, after he visits his old companions, causes him to regenerate.
a lot of times its your timing belt, if its more of a knock its could be a rod knock
that you sneezed four times
its mean to find the area and then multiply by four.
It is coming out on the 14th novenber. I read it in my Doctor Who Adventures magizine. It said that someone is returing. I thought the master because in the planent of the dead, she said: Doctor, You take care now. 'cos it is returning. Though the dark. (doctor) what do you mean? He will knock, four times. I guessed it was a man because she said, HE is returning. So there you go. :) Ok so if you look out for an advert that tells you about Doctor Who The Waters Of Mars then it says on that when it is coming out and it says 15th November check the website if you don't believe me www.bbc.co.UK/doctorwho
it means times by four or to add it 4 times together.
Knock on wood means you are hoping that it happens.
Entering a House - "Ko ko!" means "Knock knock!"
Times. Four of fives is four lots of fives of 4 times five which is 20.
That it's time to see the doctor!
knock each other out
quadruple means that the rate of a reaction has increased by four ...... and 'four times' means that a reaction is taking place four times .
That you are supposed to do something four times everyday.