somebody's mind boggles informal
something makes somebody's mind boggle informal
something boggles somebody's mind informal

The mind boggles at the amount of time they must waste.

But if it is legal, the mind boggles at the possibilities.

My mind boggles at the very idea, but I'm told that it is so.

"The mind boggles," the President muttered before he could stop himself.

The mind boggles thinking about the cost in lives and destruction.

I knew that he was right, of course, but nevertheless my mind boggled at the figures.

The mind boggles at man's progress in the last hundred years.

Well, the mind boggles, but you can see what he's driving at.

His mind boggled slightly over the concept of "real practice."

If your mind isn't boggling at that thought, it really should be.