
Which means--
The Big Bang Theory Season 7, Episode 21

It is only by opening the box
that you'll find out WHICH it is.
The Big Bang Theory Season 1, Episode 17

Because that WHICH is real...
Westworld Season 2, Episode 10

...WHICH is often the result
of unmet childhood emotional needs.
The Big Bang Theory Season 2, Episode 15

WHICH I can only watch when
it's still light out, but...
The Big Bang Theory Season 7, Episode 4