You'll never know until you cut into it! My grandfather once had a pumpkin/butternut squash hybrid decide to grow out of his compost pile. It was huge, orange on the outside, but smooth - not ribbed like a pumpkin. It was also not mostly hollow like a pumpkin would be, it was solid like a butternut squash - and weighed a ton! He had to move it with the tractor when it was ready to be eaten!