"MUCUS plug" again.
The Big Bang Theory Season 11, Episode 16
Boy, if good ideas came out of your brain
the way MUCUS comes out of your nose,
The Big Bang Theory Season 10, Episode 19
Oh, I watched a video
of the hagfish producing MUCUS,
The Big Bang Theory Season 9, Episode 9
Has your MUCUS plug popped out?
The Big Bang Theory Season 11, Episode 16