
She's my TWIN sister.
The Big Bang Theory Season 1, Episode 15

Penny, this is Sheldon's TWIN sister.
Missy, this is our neighbor Penny.
The Big Bang Theory Season 1, Episode 15

I have a TWIN sister
whose assaults began in utero.
The Big Bang Theory Season 3, Episode 17

Now, I've lived my whole life dealing
with the fact that my TWIN brother is...
The Big Bang Theory Season 1, Episode 15

but when they're TWIN primes,
The Big Bang Theory Season 9, Episode 12