Gourds like these have a hard shell, about 3 mm thick, that is rather hard to cut through. We used a loose drill bit (turned by hand) to make the initial cut. From there, a regular hobby knife (e.g., x-acto) works well. Once the soft flesh and seeds are scooped out, the hard shell can dry to make a semi-permanent display.
It's unreasonably fun to walk around with one of these in each hand, reenacting the age-old chase drama. Especially when the little yellow dude chomps a big white dot. Now who's chasing who?!?!