Just thought of this question, and I'm not looking for your 'interview answer', but I am genuinely curious. I'm also looking for an explanation if you feel like it.

Mine:

Process Dynamics & Control: I find sensors interesting and the their response has a lot more science behind it than people realize. For example your toaster oven most likely (unless you bought a fancy one) can either be 'on' or 'off', but how does it regulate the temperature? How does it ensure that it does not overshoot or become unstable? Also PID controllers are heavily used at my company and I think their different parameters are extremely interesting.

Physical Metallurgy (basically materials sciences): The amount of information available about materials is astounding and materials are selected for a reason, but why? There are a number of different reasons why your computer might use a component as a basis for its motherboard construction but do you actually know why it was selected? Something I found particularly interesting was the ways thing fail, and the different shear properties of materials.

I also realize that the title isn't grammatically perfect right after I posted this, but I wanted to include 2 classes and I didn't read the rest of it apparently. If a mod wants to fix it have a blast.