Final appearance of Bob Newhart as Arthur Jeffries/Professor Proton. In his previous episode The Proton Regeneration (2017), Newhart also appeared in Sheldon's dream on Dagobah, expressing his wish to meet in a deli while eating a pastrami sandwich. His wish has been granted here.
While impersonating the Russian cosmonaut, Bernadette says "Kak khorosho", which is Russian for "How good."
Bernadette (Melissa Rauch) impersonates a Russian physics expert. In The Gorilla Dissolution (2014), she mentioned that if she hadn't become a microbiologist, she would have gone into physics or ice dancing. She also implies that she is good at lovemaking as she is very flexible. In The Bronze (2015), Rauch's character was an Olympic gymnast who could have sex in very flexible ways.
Title reference: Raj and Howard get into a conflict when Howard is asked to appear on Raj's planetarium show.