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

...and his five TWIN brothers,
you are wasting your time.
The Big Bang Theory Season 1, Episode 16

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

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