Today is Corpus Christi, a moveable feast day in the Catholic calendar which falls on the Thursday after Trinity Sunday. In Mexico it is commonly referred to as "Día de las Mulas" (Day of the Mules). It may have received that name because, in days of old, rural people would bring their mules laden with offerings for the church. Alejandro told me that it is also the custom for parents to bring their children to church dressed in traditional indigenous attire.
So today, I took the Metrobus and the subway downtown to the Cathedral to see what there was to see.
The Cathedral was quite crowded, and indeed there were many children dressed for the occasion. I always feel uncomfortable taking pictures of little children, but there were several groups of tykes whose parents did not seem to mind the attention of photographers.
I did not see any mules today, but I have seen vendors selling little figures made of corn husks representing mules laden with offerings.