That's not the SECRET knock.
The Big Bang Theory Season 1, Episode 16
One top SECRET quantum guidance system.
The Big Bang Theory Season 10, Episode 20
Look, why is it so hard
for you to keep one little SECRET?
The Big Bang Theory Season 2, Episode 1
It's got a
SECRET ingredient.
Breaking Bad Season 2, Episode 2
That was no SECRET.
Game of Thrones Season 6, Episode 1