Black Tack Pumpkins OR puff paint! I don't like the swirls (it isn't scary at all!) but maybe I could use white puff paint (even better if it were silver glittery too) to draw on a spider web and attach one of those little spider rings.
Pumpkin-Carving Tips and Tools: Make Carved Pumpkin Last - Spray a mixture of bleach & water on the inside of your fresh pumpkin daily or coat the inside w/ petroleum jelly to keep mould & dehydration at bay.
troubled teeth jack-o'-lantern (slide and 11 more pumpkin carving ideas.if you want to bring an extra scary element to your simple jack-o'-lantern, use an array of scattered toothpicks as sharp and scraggly teeth