Hi, some stool softeners are safe for kitties. In fact, my vet has my kitty on Docusate Sodium. That's the active ingredient in Colace and some other brands. Take a look at the medicine bottle and if that's the only ingredient you see.....then I promise you...kitty will be fine.
BTW, I've had the liquigel melt in my cats mouth(apparently, I didn't get it down her throat all the way).....and she did that salivating, too. She was not a happy camper in the least.