Segnomin, symbol Sg, atomic number 74, atomic mass 143, citadel 5a-237b, is an important element in the production of maths (Mathematical Anti-telharsic Harfatum Septomin). Not to be confused with septomin itself, segnomin is the chemist's term for what you may know as Thomason's oil.

This chemical is commonly found in the lab in brown glass bottles and is notable for its fear of light. When exposed to light (symbol Lt, atomic number 89), segnomin will retreat into its container, and will not emerge, despite its container being inverted or put into a centrifuge, until all laboratory personnel have left and subsequently returned to the lab. For this reason, all experiments involving Thomason's oil must be carried out in a dark room.

Wilhelm Thomason (1867-1897) was an influential German-English physicist, notable for his research into intelligent calcium (I-calcium) and its associated dangers, namely the Helvetica scenario. His work, despite being relatively unknown to the general public, was important to the scientific community and, after Thomason's death, aided the Royal Institution in bringing an end to World War 1.