Poor thing :(
A trip in the car usually leads to the vet.
that's pure uncertainty & almost panic poor puddy (we humans like to "personalise" the reactions we see in animals, but this is not "surprised" at all)
cats (animals) can "Super" smell via their palate and at times of stress or when they are particularly interested in something they will "smell through their mouths.
Sometimes see cats do similar if there's a bird in view.
Aw, cats usually breathe with their mouths open because of anxiety or heat. Could it be that the cat felt hot that time? It might also be anxious of the whole travel… I hope it felt better when they got to their destination.
Leisa, yep distressed I'd say.