Y'know, the off-white stuff that sticks to the tip of your dilator - greasy, slightly acidic smelling paste composed of dead skin cells, lubricant and probably some bacteria, too.
Actually, I was slightly worried when bindel appeared for the first time - I thought it was due to some sort of vaginitis, but since it doesn't really smell foul, I figured it isn't dangerous. A visit to the ob/gyn confirmed this, as did a call to the surgeon. Just a byproduct of my slightly variant biology. ;)