This is indeed the sound snakes make when they have a respiratory infection.
Like others have stated, it can easily be taken care of if caught early enough. Put the snake's head to your ear and listen carefully to it's breathing. If you hear any wheezing, or clicking sounds do the following ASAP!!
* Raise the cage temp to 88-90 degrees(for approx. 14 days. use reliable thermometer down on substrate...do NOT guess)
* If temp. raise doesn't cure it, it needs to see a vet quickly for administration of antibiotics(Amikacin, Baytril)....this should NOT be treated lightly,.....if gone untreaded, it can quickly lead to the snake's death!
Hope this helped, ~Doug
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"Better to be silent and thought a fool, than to open mouth and remove any doubt!"