If you say that the mind boggles at something or that something boggles the mind, you mean that it is so strange or amazing that it is difficult to imagine or understand. The mind boggles at the possibilities that could be in store for us The good grace with which they face the latest privations makes the mind boggle The management group's decision still boggled his mind. see also mind-boggling. the/your mind boggles sth makes the/your mind boggle sth boggles the/your mind if your mind boggles when you think of something, it is difficult for you to imagine or accept it (Perhaps from bogle; BOGEY)
If you say that something is mind-boggling, you mean that it is so large, complicated, or extreme that it is very hard to imagine. The amount of paperwork involved is mind-boggling. = unbelievable. difficult to imagine and very big, strange, or complicated