Sometimes a dog just doesn't feel like it. Feel like what, exactly? Anything. So he just lies there, on the ground, and if you want him to move, well, good luck with that.
I've seen many brides and grooms walk down the aisle, and all of them have gone off without a hitch. When it comes to the flower girls, who are usually their very young nieces, it's not always so smooth.
They hesitate. They go the other direction...
By now you've probably seen at least one video of a soldier or Marine returning home and seeing his dog for the first time. It's one of the things the Internet does that really, genuinely tugs at your heartstrings.