What Causes Spit On Penile Shaft After Having Sex?

I noticed that after sex with my wife on consecutive nights a very small split (2-3mm) on the shaft of my penis near its head. It looks a lot like a paper cut. About a year or so ago my wife had (at the time) undiagnosed thrush and I contracted a minor case of oral and genital thrush....so not sure if related to that or not. There is no discharge, no pain during urination - the only physical symptom is this small cut and a very very small amount of discomfort. (as I d imagine any cut would have)