Breathing signs come first
Snakes conceal illness well, so respiratory noise is one of the clearest alarms you will get. Whistling or clicking with each breath, breathing with the mouth open, mucus bubbles along the lips, or a snake holding its head raised to breathe more easily all mean a vet visit — respiratory problems in snakes progress, and early attention is a very different proposition from late. One exception keeps you calm: a slight whistle during a shed, when loose skin around the nostrils flutters as air passes, can be innocent. Noise that persists after the shed completes is not.
Skin, shed and mouth
A healthy shed comes off in one piece, with clear eye caps visible in it. Retained shed — especially cloudy caps stuck over the eyes — needs attention: raise humidity first, but book if the caps survive another shed or the eyes look dented or infected. Check the mouth if you catch a yawn: sores, redness, pale cheesy patches or uneven swelling around the jaw are vet signs, not home-treatment signs. Visible mites justify a visit alongside your enclosure clean-out — look for tiny dark specks moving at the scale edges, white dust-like droppings on the snake's skin, or a snake that suddenly soaks in its water bowl for hours to drown them.
Feeding patterns and the body
Judge refusals against the species and the season. Many snakes fast naturally in cooler months, when coming into shed, or as mature males in breeding season, and a settled adult in good body condition can skip meals that would be alarming in a hatchling. Book when refusals run well past the snake's own established pattern with visible weight loss along the spine, when meals come back up more than once, or when swelling appears anywhere along the body. A single regurgitation after a too-large meal or a cold night usually needs husbandry adjustments; a snake that cannot keep meals down at all needs examining.
The urgent list and the baseline visit
Prolapse, injuries, burns from unguarded heat sources, and a snake that lies limp or cannot right itself are same-day problems — phone ahead and travel with the snake secured in a ventilated, escape-proof box. Otherwise, arrange a baseline visit when a snake is new to you, taking a droppings sample once it produces one. That visit gives the vet a healthy reference point and gives you a relationship with a clinic that actually sees snakes, which is worth far more arranged calmly than searched for in a panic.
Logging every feed, shed and refusal in KinsLe's Pet Passport gives the vet your snake's real history, which matters because a snake's story is written in its patterns.