I asked my friend what he said to indicate that something isn't so difficult. He said: I say, "this isn't rocket science."

I asked a rocket scientist what he said to indicate that something isn't so difficult. He said: I say, "this isn't nuclear physics."

I asked a nuclear physicist what he said to incicate that something isn't so difficult. He said: I say, "this isn't brain surgery."

I asked a brain surgeon what he said to indicate that something isn't so difficult. He said: I say, "this isn't rocket science."