When Brains falls under The Hood's influence, he collapses and between shots his glasses simply disappear. They are subsequently shown to have fallen off but the action is not seen on screen: one moment the glasses are on his face and the next they have vanished.
This marks the first time a Thunderbird machine was involved in battle.
This episode was one of the rare cases that Alan did not appear at all. John was at home so that puts Alan in space.