As frequent readers of this blog and people who have met me personally know, one of my main interests is the use of language and I speak both Finnish and Spanish with my wife (with a liberal sprinkling of English depending on the subject).

With her we've found out that who speaks better the language of the other depends on the day.  Sometimes I speak Finnish better than she does Spanish, sometimes it's the reverse.  Is it just because of general tiredness or some other reason?