When we take her in the car, my cat opens her mouth for like 5 min... no sound. What is that?

She is taking in deep scents to help her analyze the situation, cats use their sense of smell more than humans do. Your cat is using her Jacobson's Organ and the Flehman Response.

Cats (along with snakes and a few other mammals) have a magnificent organ called the vomeronasal organ, most oftenly known as the Jacobson's Organ. It is located inside the mouth, just behind the front teeth, and connects to the nasal cavity. Opening his mouth slightly enables the Jacobson's Organ to open up the ducts connecting to the nasal cavity. The appearance of the cat as he brings air into the Jacobson's Organ has sometimes been likened to a "smile," other times to a grimace.

Whenever a cat "open mouth breathes" it usually isnt a good thing. This is usually the first indication of stress. I worked in an animal ICU for a few years and when kitties did this, it usually meant bad things. My cat once sniffed something in the house that made him somewhat open his mouth a little more than usual, but that was only because he was taking in MORE scent than just his nose was able to...But when you take her/him for a car ride, try to keep the air cool, the sound low and keep her in a cozy kennel to try and lower the amount of stress...Take corners and speedbumps slowly, and maybe try talking to her as well.

Yeah!! That is a great question! When I wake up in the morning to go to the bathroom my one cat Oreo follows me around with his mouth open like he's about to meow but no sound comes out at all. LOL it's kinda cute! I think its just a cat thing... I hope...

Isn't that when they are trying to take in extra smells for some reason? Also sometimes my cat meows but she barely makes the noise, so sometimes it's just a little squeak. It's the cutest thing ever. And in the morning when she's waiting for me to get her wet food, she has the highest little teeny meows and her tail is super high. :)

a cat will do that when the smell something good or bad the males will do that when the smell a female in heat or another males pee.It's a smell them smell and you might not smell it wipe the car sets down with bleach let air out and try that bleach kills smells and Pee

the roof of a cats mouth is how they determine where they are who's been there how long ago where they here yeah it's actually quit interesting

Is she panting? My cat, when I take him into the car, stresses out so bad he beings to pant heavily and spaz out. If she is panting you should stop taking her for car rides as it is extremly stressfull for her.

Maybe she is an adrenaline junkie. Go faster and see if she opens it more or makes noise. Maybe you could get her to say "Faster!"