Robert Patrick is wearing the same outfit his character, the T-1000, wore in Terminator 2.
The scene where Happy is drilling into Walters Skull to relieve the pressure with a drill is quite fitting as Elyes Gable previously stared as Doctor Gurpreet 'Guppy' Sandhu, in the longest running UK medical drama, Casualty. In one S21 E1 his character, while on a visit to Cambodia, successfully performs the same procedure also using a hand drill