Write a 2000 word scene from a novel where NAME_1 a shy, skinny 15-year-old boy is asked by his 12-year-old little sister NAME_2 to film her and her friend NAME_3 doing the watermelon challenge for TikTok. He has no idea what she's talking about but she leads him out to the backyard where her friend is waiting with a stack of watermelons. Both girls take of their t-shirts and shorts to reveal they are wearing swimsuits underneath. The boy is shocked by how thick and muscular the two pretty young girls look, presumably from all their gymnastics training. He has to film as first his sister and then her friend, place a watermelon between their thick thighs and then squeeze with all their might, grunting with exertion until finally the watermelons split and explode in a shower of pulped pink flesh. Focus on the shock of the boy at the unexpected display of youthful feminine might and how it makes him feel, not least due to the sexual implication of the challenge. NAME_2 then takes the phone from him and tells him it's his turn to do the challenge. He is reluctant but NAME_2 and NAME_4 him into it. As NAME_2 starts filming, he gives it everything he's got, but is dismayed to find that he lacks the strength to even make a crack in the melon. Describe how emasculated he feels and how he protests unconvincingly that they must have tricked him by already weakening theirs. The girls scoff and NAME_2 grabs his intact watermelon from him and effortlessly crushes it between her thighs, even quicker than the first time. Describe how he feels.