I agree, it sounds like a practical joke.
If a hen releases two yolks at the same time you often get double yolked eggs.  If that extra release is spaced out a bit you can get two eggs in one day.  It happens more often than people think but it's not real common.  As long as it's not common it's not a problem.
The hen normally makes a certain amount of shell material in a day.  If she lays an unusually small egg the shell can be unusually thick.  If she lays an unusually large egg, like a double yolked egg, the shell can be fairly thin compared to normal.  If she lays two eggs in a day the second one may be shell-less or really thin shelled. Or it may not.  If two eggs are in the shell gland at the same time the eggs may show "scars" or marks when they are laid from where they were touching.
If she is laying brown or green eggs, the hen normally makes a certain amount of "paint" to color the egg.  A second egg might be pretty light-colored compared to normal. 
It is possible for a hen to lay more than one egg a day but they are often not both normal.  When that happens many hens skip laying the next day.  Sure sounds like a practical joke to me.