[Cazador]

Blood samples can show signs of a few parasites, but they're by no means ideal or comprehensive. A fecal sample is the way to go. Internal parasites are easily treated, but I don't want to get you all scared. Your snake is just a bit skinny, which could simply mean it's been underfed.

I'd just weigh them (to the gram, if possible) and feed them twice a week for a month. Then reweigh them, and see if it's gained weight. Also, keep an eye on the stool just in case you see a roundworm or tapeworm segment. If the stool is very runny, without shape (like the brown part isn't turd-shaped), or it's VERY smelly, you'd get an indication that it might have internal parasites. These, too, are just clues, but a vet would be able to tell you for certain, if you take in a fecal sample.

Rick