I took my rabbit out today in the car. He was extremely scared (he never takes car rides very well). There were several things he did that made me nervous, though.
1. This was the worst one: he was clicking his teeth! It wasn’t a grinding noise, it was as if he was opening and closing his mouth to make his teeth click together, or like the clicking of the tongue. It almost sounded like a tune, to be honest.
2. He was shaking/shivering. It is normal for him to shake when he’s scared, however. Sometimes when he runs a lot, he sits down and shakes from breathing so hard, but I know that’s because he’s happy.
3. He repeatedly licked his lips. It was hot outside, so I assumed he was thirsty. I offered him water, but he refused, so I wiped his mouth with water for him to lick it off (it kind of worked).
At one point, he opened his mouth and I freaked out… I thought he was going to scream or something. Turns out it was just a cute ‘lil yawn… 
He is totally back to normal now that we’re home. He hasn’t eaten anything or used the washroom yet, but that’s probably because he’s had a long day and just wants to sleep.