在英文中，可以用以下几种表达方式来描述老虎正在吃东西：

The tiger is eating something.
The tiger is feasting on something.
The tiger is chowing down on something.

这些表达方式都可以表示老虎正在大快朵颐地吃东西。

下面是一些英文例句，并附上中文翻译：

I saw a tiger eating a deer in the zoo yesterday. 昨天我在动物园看到一只老虎在吃鹿。
The tiger was eating a large piece of meat when we saw it. 我们看到老虎时，它正在吃一大块肉。
The tiger was feasting on a fresh kill when we saw it. 我们看到老虎时，它正在大快朵颐地吃着一头新猎杀的动物。