这只斑马不吃草的英文表达是 "This zebra is not eating grass."

这个表达的来源是因为斑马是一种草食动物，通常会吃草。如果有人发现一只斑马不吃草，就可以用这个表达来描述这种情况。

下面是一些英文例句和中文翻译：

"I noticed that the zebra in the zoo wasn't eating any grass. I wonder if it's sick."
(我注意到动物园里的斑马没有吃草。我想知道它是否生病了。)

"The zebra at the Safari Park refused to eat the grass that the keeper offered it. It must be picky."
(野生动物园里的斑马拒绝吃看守员给它的草。它一定很挑剔。)

"I've never seen a zebra that doesn't eat grass. This one must have a special diet."
(我从未见过不吃草的斑马。这只一定有特殊的饮食。)