cowlick & comfortable as a cow

日本は他の国ほど酪農は盛んではないので中国故事からの言い回しを除くと、牛馬羊などの単語を含む表現は、犬や猿を含む表現と比べて多くはない気がします。The Glass Menagerieの中に "cow" が二つ次ぎの文の中に出てきたのでそんな事が頭に浮かびました。
AMANDA: I'm brushing that cowlick down! [She attacks his hair with the brush.]
文脈からすると "cowlick" は前髪の気がしますが、辞書で確認します。
・Collins English Dictionary: a tuft of hair over the forehead: He had steel-grey hair that had been neatly combed to one side, although a tiny cowlick at the front gave him a slightly aristocratic air.
・Cambridge English Dictionary: a bit of hair that always sticks out on someone's head
・Oxford English Dictionary: a lock of hair hanging or projecting over a person’s forehead: his hair was cut short with a cowlick dropping over at the front
・Dictionary.com: a tuft of hair that grows in a direction different from that of the rest of the hair: She had a distinctive cowlick on the right side of her forehead and a birthmark on her stomach---possibly on the left side.
癖毛を指している様事ですね。
The Glass Menagerieに出て来たもう一つの牛の表現を引用します。
JIM: So am I. Comfortable as a cow!
闘牛などを別にすれば牛はのんびりと草を食べている印象があるので、なんとなく分かる気がします。