
I believe this is an extension
of the death METAPHOR.
The Big Bang Theory Season 2, Episode 8

You know what? I'm thinking Howard
wasn't making a back-scratching METAPHOR.
The Big Bang Theory Season 2, Episode 16

I believe the back-scratching METAPHOR
describes a quid pro quo situation...
The Big Bang Theory Season 2, Episode 16

Yeah, me, too. I was stuck for a METAPHOR.
The Big Bang Theory Season 9, Episode 12

Luckily for you,
that's where the METAPHOR ended.
The Big Bang Theory Season 1, Episode 15