「そんな大きなスイカ一人で食べられないでしょ。」
= Sonna ookina suika hitori de taberarenai desho.
= You know you are not going to be able to eat a watermelon that big by yourself, right?
「食べられないことはないよ。」
= Taberarenai koto wa naiyo.
= I wouldn’t say it is impossible. (I could eat it.)