Sensurround is a short-lived technology used to enhance the audio of films, by adding loud bass speakers to provide audio that is felt as well as heard. It was originally designed for the 1974 film Earthquake, where it was used to augment the quake segments. It was last used for the Battlestar Galactica compilation film "Mission Galactica: The Cylon Attack", in 1979. Thanks to its rather gimmicky nature, and the fact that both are supposed to enhance the feeling of being there, Mark Kermode often references it when talking about Three'd.
Specifically, Mark drew this parallel when Monsters Versus Aliens was on release, saying that film had to be seen in 3D in the same way Earthquake had to be seen in Sensurround. There then followed a fine instance of Wittertainment at its most Wittertaining as Mark asked Simon Mayo if he remembered Earthquake coming out. When Simon replied that he did not recall this, Mark insisted Simon did remember it (he had argued something similar earlier in the episode when, while discussing Crank 2, Mark had referred to the U2 heads that used to be on TFI Friday, and Simon hadn't remembered those either). Mark then asked Nick Duncalf if he remembered Earthquake coming out. Nick said he didn't remember it, but knew it was made in Sensurround - "everyone knows about that Simon." Simon pointed out that there is a difference between knowing about something and remembering it, and had he been asked if he knew about Earthquake he would have said yes. Mark quoted the words of Douglas Adams on Ford Prefect - "one of those people that you could not see for the longest time, but when you did they were immediately annoying" - to which Simon replied, "what’s that got to do with Nick Duncalf?"