I stuck my nose under my cat's belly and smelled him but he didn't like it.
My cat doesn't like it when I bury my face in the fur around his stomach.
ーI stuck my nose under my cat's belly and smelled him but he didn't like it.
「猫のお腹に鼻をうずめて匂いを嗅ぐと、彼は嫌がる。」
stick one's nose under my cat's belly を直訳すると「猫のお腹の下に鼻を突っ込む」となりますが、この場合は「猫のお腹に鼻をうずめる」というニュアンスです。
belly「お腹」
ーMy cat doesn't like it when I bury my face in the fur around his stomach.
「うちの猫は私がお腹の周りの毛に顔をうずめるのを嫌がる。」
bury one's face in ... で「…に顔をうずめる」と言えます。
fur「柔らかい動物の毛」
stomach「お腹」
ご参考まで！
カナダ 
