Both the professor and his wife could speak a bit of English and Spanish, and they mixed all three languages together all evening--often within the same sentence. For example, as we pulled into the empty university parking lot, they had this exchange:
Professor: Only one car...
Wife: Domingo da mon!
[Translation: Duh! It's Sunday!]
It took about a half hour for the professor to set up the lecture slide show on his laptop, and then he read through it while I marked corrections on the script. The topic was using various types of spectroscopy to examine the feldspar contained in granite to ascertain factors such as water and mineral content, information that can be applied to areas like mining for ore deposits. It was all "wavelength dispersive electron probe microanalysis" and "micropores are produced by dissolution-reprocipitation during low temperature hydrothermal reactions"...for an hour and a half.
Boy, am I glad I had a geology field course in college. I actually managed to understand a large chunk of it.
Afterward, the professor surprised me by giving me an envelope of cash to pay for my time and transportation AND they then treated me to dinner at a family restaurant. We continued to chat about a bunch of things, still in three languages mixed together. (Well, techinically I was only speaking English, but I was listening to all of it...) At one point, the professor wanted to know how to say a particular word, but he didn't know the phrase "how do you say?" in English--only Spanish was coming to mind for him. So he essentially asked in Spanish, "¿Cómo se dice 'cómo se dice'?" That was good for a giggle.
I wound up getting home at around 9:30pm, so it was a full evening for me.