Super Green Watermelon
From the Super Mario Wiki
Super Green Watermelons are watermelons (with green skin, red flesh, and black seeds) found in Super Mario World 2: Yoshi's Island and its remake Yoshi's Island: Super Mario Advance 3. If a Yoshi eats the Super Green Watermelon, Yoshi can spit seeds. Grinders have many Super Green Watermelons, some half-eaten, which only let a Yoshi spit out half as many seeds as a full melon. Grinders use the watermelons to spit seeds. The seeds have the same effect on enemies as an egg.
Yoshi and a Bandit duel with spitting Super Green Watermelon seeds at one another in the Mini Battle minigame, Watermelon Seed Spitting Contest. Whoever spits the most Watermelon seeds at one another until one's HP runs out as shown on the HP bar wins the minigame.