You could try gently shaking your plant on it's side to try and get any lose seeds to fall out. (don't be to rough with it) Your plants whole goal in life is to grow big and produce seeds to pass it's genetics on and keep the strain alive. Once your plant has been pollinated and forms seeds those are the only seeds it'll produce (unless you really stress it out and force your plant to herm, but then the seeds wont be the same as the ones you got form pollinating).
Now if you have a plant that hasn't been pollinated then if you let the plant grow past it's prime then it'll produce seeds as a last ditch effort to pass it's genetics along, but you might have a lot of hermie seeds.
If I get seeds I usually wait until the plant is ready to give me the seeds or I cut the bitch down and take her seeds during drying/curing.