Urodynamic tests

A bit confused by urodynamic test yesterday. Nurse said that leakage was evident because the pad had got wet. I wasnt wearing what I take for a pad as such, but I was lying on an absorbent bed pad thing. I dont see how this could have got wet from my willy though as it was full of tubes used to fill my bladder with water and one which I think ran to a computer. Did she mean leakage from my bottom as she put some kind of tube thing I did not see up my bottom and I felt something bubble out a couple of times at some point - maybe water was squirted inside I dunno. Anybody understand these things, how they work?