Jim,
you actually spray the lemon/water combo into the dog's mouth and that usually gets them to close it. And, yes, it's totally harmless.

I usually just put a finger in the mouth to get them to close it. Of course, I deal with show dogs and I'm not sure I'd try that will dogs that weren't used to it .

You might also try an ice cube or just very cold water in a spray bottle again just to spray in the mouth to get them to close it. Panting is how dogs sweat so if you can cool off the mouth, it usually stops them from panting for a few seconds. But be quick .

If that doesn't work, find the best angle to shoot them with the tongue hanging out. Some dogs look very sweet with their mouths open.

Jim