Well as far as spit on the tongue goes, any water that doesn't boil off remains in contact with the tongue/cheeks, conduction being way faster that radiation at

Well as far as spit on the tongue goes, any water that doesn't boil off remains in contact with the tongue/cheeks, conduction being way faster that radiation at 37c any spit that did freeze due to evaporative cooling would thaw out again very quickly. It's different for urine which lacks the continual heat source. If you had a mouthful of water, instead of a thin sheet of spit, you'd likely end up with an ice cube for a while.