To him, the shape of the rabbit's nose and the mouth looked like the letter x.
He perceived the rabbit's nose and the mouth as an x-mark.
ご質問ありがとうございます。
① "To him,"＝「彼には」
"the shape of the rabbit's nose and the mouth"＝「ウサギの鼻と口の形は」
"looked like the letter x."＝「ｘの文字のように見えた。」
（"letter x" の代わりに "x-mark" とも言えます。）
② "He perceived the rabbit's nose and the mouth as an x-mark."＝「彼はウサギの鼻と口をバツ印として捉えた。」
ご参考に。
"He thought the shape that a rabbit's nose and mouth make looked like an x."
"He thought the shape that a rabbit's nose and mouth make looked like an x."
"he thought ~" 「彼は～と思った」・「彼には」
"the shape that ~ make" 「～の形が」
"a rabbit's" 「うさぎの」
"nose and mouth" 「鼻と口」
"looked like ~" 「～のように見えた」
"an x" 「ばつじるし」
アメリカ合衆国 
オーストラリア 
