Crab bubbling at mouth area?

[troppo]

In my large tank, I keep the temperature warm and the humidity between 80-85% because there's a jumbo Straw in the tat.

On occasion when I've picked up one of the crabs, for some reason they've not wanted to be picked up and I hear a faint crackling noise coming from the crab and see little clear bubbles coming out from between the mouthparts, so I put the crab back in the tank because I think that some crabs just get scared/stressed out by being handled.

Have had it happen with my jumbo Straw(Strawzilla), the new Blueberry(Macca) and with my Aussie crab(Luke) who passed away months ago from being attacked by another crab and not making it through his molt.

Once it happened to an Aussie crab(Eeyore) after he was attacked by another larger crab and rolled onto his back. When I went to rescue him from the attack, he was already making crackling noises and blowing clear bubbles.