Ah ito siguro from the liver talaga! Ang dark fiber-like bits ay common pag kumain babies ng iron-rich foods like liver, it's basically undigested bits ng meat fibers showing up sa poop, totally normal at walang worry. Since 10 months na siya at kumakain na ng solid foods, makikita mo talaga yan lalo na pag maraming liver or red meat, basta consistent pa rin ang poop pattern niya at masaya pa rin siya, you're all good! Though if worried ka pa rin or nakita mo pa ring suspicious stuff after ilang days, okay lang i-mention sa pediatrician just to be sure.