Howard refers to Isaac Asimov's Three Laws of Robotics which were introduced in his 1942 short story "Runaround".
Johnny Galecki and Sara Gilbert previously played boyfriend/girlfriend, and then husband/wife, on Roseanne (1988).
After Sheldon (Jim Parsons) asks if he would be bound by Asimov's three laws of robotics, Howard (Simon Helberg) covers only the first two before saying "I smell a robot".