boggle at (something)
To gape or gawk at something; to struggle to accept or understand something. I boggled at the very generous salary offer and hoped it wasn't an error. When my wife surprised me with a new car, I could only boggle at it in our driveway—I couldn't even speak!
boggle at something
to be amazed at something, particularly something large or surprising. The audience boggled at the size of the loss. I boggled at the damage to my car.