Guess everyone else knows this except me. But in case there's someone out there who's as slow as I am:

It's NOT a good idea to carry around sandwiches in the outer pockets of your handbag, especially meat sandwiches, no matter how carefully wrapped, the day before you fly back to the U.S. No matter that the sandwiches are long gone, wrappers thrown away, no matter that you have absolutely no food with you on going through agricultural station. Agriculture has sweet little dogs, but it's not an optimal time for them to come up to you and indicate they find something about you of possible interest. Don't ask me how I know this.

Told the official he was welcome to inspect my handbag. But I guess he realized anyone who looked as flustered as the way I did would be slim pickings, so he waved me on by.