So the immediate response that you will find it in their mouths so you may get swelling up of the tongue. The signs you will see is irritation, probably drooling. They may go and open their mouths because they are uncomfortable, they may be sick, trying to bring it back up again. And in those cases, if you can have a look in their mouth and see if there is anything that you could remove if there was something that had a toxin on it that you could then take out, you may want to get some water and flush out the mouth if possible. In most cases, I would say the animal probably would not let you do that but if you can then flushing out the mouth would be a good thing to do.
If you find any burns on their skin that they have been licking, try and prevent that from happening either by covering that or in some cases you may have a Buster collar accessible. Or the plastic lampshades, you can put that on your dog or cat to prevent them from persistently licking out the area that you may be concerned about while you are transporting them to a vet.