What you are looking for is fog. That's the point when the developer shows something from nothing, or in DigitalIze - noise. Look at any of your negitives, they all have a varying degree of it.
To demonstrate, take some unexploded ( ) film and put it in your developing can. Use PQ or Dektol 1:1 (or the strongest of whatever you have) and do a time of 20 mins or so. Fix it and have a look. That would be fog.