Previously on
The Big Bang Theory...
The Big Bang Theory Season 12, Episode 18
♪ That all started
with a big BANG ♪
The Big Bang Theory Season 7, Episode 6
Previously on
The Big Bang Theory...
The Big Bang Theory Season 12, Episode 12
♪ Bang! ♪
The Big Bang Theory Season 5, Episode 20
♪ Bang!♪
The Big Bang Theory Season 12, Episode 21