You and me, both!
A few weeks ago I read that line for the first time. I asked what it meant, why the mule grinned.
A good Southern Freeper said it was because the mule folds his lips up so's not to get pricked by the briars, and he looks like he's grinning.
I thought that was the funniest thing I had heard in a while.
That's true. And a horse will do the same. Some love blackberries and raspberries and will pick around briars for the fruit.
Sounds much better with the mule line though. Especially with Kerry's face.