
If the two of you engage in intercourse,
this will create the biochemical REACTION...
The Big Bang Theory Season 2, Episode 9

...or drinking coffee while driving
reduces one's REACTION time...
The Big Bang Theory Season 2, Episode 5

Leonard, what if you have
an allergic REACTION...
The Big Bang Theory Season 8, Episode 9

in which I looked up
the REACTION rates
The Big Bang Theory Season 7, Episode 6

No visible REACTION.
The Big Bang Theory Season 7, Episode 5