His ears are laying flat on the side of his head because he's really frightened about something,
この場合、次のような言い方ができますよ。
ーHis ears are laid back because he's so scared.
「猫は驚いて耳が倒れている」
ーHis ears are laying flat on the side of his head because he's really frightened about something,
「猫は何かにすごく怯えて耳を頭の横で平らにしている」
ご参考まで！
カナダ 
