Yawning can also be indicative of a snake just stretching his mouth, tasting the air etc. I've noticed every one of my snakes doing this behavior after we bring them out for some handling, or they are waking up at night to cruise around.

If he pooped on you, the hickup could have been a fart. Snakes are more likely to fart.

If he pooped on you, he was likely stressed. I have never once been pooped on by a snake. I have been peed on by a snake that was in distress.

Watch him carefully, review your husbandry and look for the tell tale signs of whistling, popping, wheezing, druel from his mouth or on the sides of the tank. Look for him to sit with his head raised, or his back arched for long periods of time.

If he shows any of these signs, take him to a vet and request a swabbing and culture.