Blanky (Ian Hart) mentions his previous four year ordeal on the Ross expedition, after Sir James Clark Ross (Richard Sutton) who appears at the very beginning of the series and during the Admiralty scenes.
Laudanum was a oral solution of about 25% ethyl alcohol and 10% powdered opium (equivalent of 1% morphine). It was extremely bitter, the alcohol was added as a sweetener. Laudanum contained almost all of the different alkaloids of opium, including the two most common which are codeine and morphine, Laudanum's high morphine concentration made it very potent and highly addictive. Laudanum has been used since the 1500's as a painkiller and cough suppressor, especially before the discovery of the method of extracting codeine and morphine from raw opium in the mid 1800's. Until the early 1900's Laudanum was available without a prescription but after the increasing number of Laudanum addicts and with soldiers coming back from World War I addicted to morphine and heroin (especially heroin) the government decided to make all opioids available by prescription only and pharmaceutical production of heroin was discontinued. Then in 1970 the Controlled Substances Act was passed which placed most opioids in the strictest category of controlled substances: heroin became a schedule I controlled substance (meaning it had no recognized medical uses and couldn't be prescribed) and potent opioids like raw opium, Laudanum and morphine were made schedule II controlled substances which are the most regulated medications that can be prescribed and are strictly monitored and cannot be refilled except with a new prescription each time.
The song that Lady Silence sings before cutting out her own tongue was composed by the actress herself, Nive Nielsen.
This episode is set two weeks after the events of the previous one.
Fitzjames is seen wearing a roman soldier attire. Tobias Menzies portrayed Brutus Caesar in the TV show Rome (2005).