Frequently used phrase:-

"I'll tell you what I don't know."  I've been asked "many a time and oft" (but NEVER in the Rialto)  "How can you, if you don't know?"  Quite easily, watch.

"I don't know what a Yew Flower looks like."  Do you? 
Here we have 4-5-6 Yew Berries - I know where they are. 
    I have not the slightest idea how long we've had it, but it predates my owning a digital Camera; maybe by a decade or more, if you see what I mean.
    Must keep a better Eye on it and see if I can find one.