Heh. Yeah I do ask it in that way and I've had a couple interviewees be cheeky and go right down to electrical signals. That's when I can see they have a bit of a sense of humour and aren't nervous. It also breaks the ice. However, I typically interrupt them and go as low as DNS routing packets and its ilk.

The reason I interrupt them when talk about electrical signals starts (or, as you mentioned, typing a key), is that I mainly hire for Web development positions and would like candidates to understand how the Web works. This knowledge is especially important for when things break down. Knowing how electrical signals work would be useful if you had to do hardware, networking, or anything else, but I just want to know that a candidate isn't just creating Web services without realizing that latency exists because of DNS routing and network hops.

Edit: clarity