DO NOT ASK YOUR DOG TO DO IT!
Image and advice from WikiHow.
Since the problem involved two toilets and two bathtubs, it was too big for me to handle, so the plumbers are here now trying to unclog the plumbing. Bless them for coming quickly. Unfortunately, one of the toilets had been used before it overflowed. I turned off the water supply quickly, so not too much spilled over onto the floor. Still...eeeww.
Grandpère is gone for most of the day with his cell phone turned off, but it's probably best that he's not here, since he's excitable about this sort of thing. Best to let the plumbers do their thing without him hovering over them in a state of nerves.
What a start to the holy day. Things can only get better, right? Please say, 'Yes!'
UPDATE: The problem is fixed. There was a blockage in the pipe that runs through our yard to the city line. The roots of two crepe myrtles planted over the pipe may have contributed the blockage. We have a decision to make.
We have wonderful plumbers. For minor plumbing malfunctions, they may take a while to come, because they're much in demand, but when there's a serious problem, they come quickly. It doesn't hurt that the same plumbers installed the plumbing in the house 28 years ago.