RuBisCO
RuBisCO
[Person in background (out-of-frame) screams out this word over all 3 panels.]
[Cueball is working on a laptop at a desk. Megan is reading a book in an armchair.] Person 1: RIBULOSEBISPH..
[In a frameless panel, Cueball has stopped working. Megan has stopped reading, and is holding her book.] Person 1: ...OSPHATECARBOXYL...
[Cueball continues working. Megan resumes reading her book.] Person 1: ...ASEOXYGENASE! Person 2: Oh, Sorry! Megan: Man, chemists pick the worst safewords.

Safe words are designated words for sexual play which are meant to be called if one partner is uncomfortable with the way things are proceeding as alternatives to simply saying "no" or "stop", which may be used to express playacted reluctance by a submissive partner who actually wants to continue. Calling the pre-chosen "safe word" would be a sign to stop. To prevent accidental usage, people generally pick words that they wouldn't normally use, such as "Pineapple" or "Hedgehog." In the case of this comic, the characters are chemists, and the uncommon word they happen to have chosen is Ribulose-bisphosphate carboxylase oxygenase , also known as RuBisCO (which actually isn't a very uncommon word in the scientific world, as it's the most abundant protein on earth, but it would be uncommon to use the full word). However, the length of the word makes it impractical for a safe word, as it would take too long to say; indeed, using the shorter form "RuBisCO" would normally be a fine safe word.
The title text mentions Bruce Schneier , a computer security professional, and public keys which is the publicly known half of public-key cryptography , which uses two mathematically linked keys to decrypt information. The joke is that Schneier considers safewords as a type of security and thus believes they are not safe enough and recommends the key signature. However, whereas it takes a long time to say RuBisCO in full during your submission, it would be impossible to use any public keys to stop your partner.
Randall later in 1128: Fifty Shades referenced the book Fifty Shades of Gray which made the concept of 'safe words' perhaps more widely known to the mainstream public. Here the word is very short: Red.
[Person in background (out-of-frame) screams out this word over all 3 panels.]
[Cueball is working on a laptop at a desk. Megan is reading a book in an armchair.] Person 1: RIBULOSEBISPH..
[In a frameless panel, Cueball has stopped working. Megan has stopped reading, and is holding her book.] Person 1: ...OSPHATECARBOXYL...
[Cueball continues working. Megan resumes reading her book.] Person 1: ...ASEOXYGENASE! Person 2: Oh, Sorry! Megan: Man, chemists pick the worst safewords.
