Frog Question

Can any one help me.
I am digging an extension to my old pond as the old small one leaked last year and I have been left with a muddy hole.
After removing the old liner which still had a small amount of water/grass/mud in it which spilt out onto the ground I was preparing for the extension and left a deepish puddle. When I returned to continue next day the water had drained away and I was surprised to find a frog in the bottom Which was covered in a mass of jelly.
A friend said when they hibernate in mud they protect themselves in this jelly. It was the first time I'd heard of this can anyone enlighten me on this.