I think Linds covered it the best...except that loud exhaling doesn't always mean they don't like being handled. They have very long lungs and your constant moving and adjusting your grip will cause them to kinda burp air out that sounds like a soft hiss... I have been doing rescue rehab work with reptiles and other animals for well over 20 years. I get far more false RI symptoms brought to me than actual RI....People are very quick to want to treat with Baytril or other antibiotics at the first hint of symptoms. This is bad. Don't do that! young snakes under a year old shouldn't be treated for antibiotics and older snakes can USUALLY be treated without them by reducing humidity to near dryness and raising the temps to right at 90 degrees and keeping them warm 24/7 for a week or so. A quick easy check to see if there is anything to be concerned about is to listen to the side of the snake about 1/4 to 1/3 down the body by placing your ear against his side...listen for raspy wheezing or clicking sounds...Like Linds said though, it is not unusual for this and/or whistling to happen during the preshed days so if he is about to shed...wait it out and check again. You don't have to wait for snot bubbles to appear nor do you have to actually open a snake's mout to check for excess mucous...gently squeeze the snout and lower jaw flat shut with your thumb and forefinger..If there is any excess mucous...bubbles will appear in the nostrils. Even this may be a false symptom...did the snake just take a drink of water? If you are sure your snake has an RI and unmedicinal treatments have failed to work and you feel an antibiotic is important...first make sure the snake is over a year old...make sure the snake is well hydrated. antibiotics dehydrate and an already dehydrated snake will likely drop dead soon after an injection of antibiotics. Make sure the shot is given in the upper 1/3 of the body even if a vet is doing it....many vets are clueless and are blundering through these things. A shot given in the lower 1/3 will go right to the liver and do some serious damage there. Many vets also figure a dosage somewhere between 5 mg per kg to 10 mg per kg and give a series of 3-4 on an every other day schedule. This is not too bad a plan really but I spoke with the manufacturers of Baytril and got a better planned assault on fighting bacterial infections...10 mg per kg booster shot for the first injection followed by 3-4 every other day shots at 5mg per kg is what was recomended to me by the people who should know best. Please pass this on to your vets and other herpers who might care. Also make sure you know how to figure the proper dosage before attempting any home medications. I find way too many people thinking that 10 mg means 10 cc of actual fluid from the bottle. baytril comes either 22.7mg per cc or 100mg per cc so be careful and make sure and double check your math. the formula is simple but also easy to screw up.
if using regular old baytril from most vet offices, it is 22.7 concentration. If you want 10 mg of baytril for a 2 kg snake... 10 x 2 = 20mg of baytril...20 divided by 22.7 = .88 which can be rounded up to .9 or 9/10ths of a cc
I know I went a bit overboard but since RI was brought up I was certain that treatments would too and these are just some things you need to know to keep your animals healthy even if you rely on vets for everything...DO NOT be afraid to question your vets knowledge and experience. Even the best herp vets out there still don't usually see many reptiles as compared to cute fuzzy animals.