As keen as mustard or as keen as a kitten
Keen as a been makes more sense. Who the heck would say keen as a lemon? One must consider the relative intelligences of the vegetable matter. Is a bean, in fact, more keen than a lemon? Could lemons not be a misunderstood fruit, perhaps with unrecognized wit and wisdom? Is someone less keen just because they are sour and yellow? Perhaps we should reconsider the traditional simile.
With these examples, you could replace the ones that have 'like' with 'as' and it will still be a simile, and vice versa. Silent like a fox. Sneaky like a fox. Sly like a fox. As red as a fox. As thin as a fox. As keen as a fox.
A simile.
A metaphor
As quick as a wink is a simile. ----
It is a simile.
simile It is an example of a simile (uses like or as). A simile in itself though is a type of metaphor.
simile
that man
It is a similie as you are comparing (something) to how sly the fox is. A similie uses the words "like or "as".
simile
simile