midnight
`` Grass cutting ? '' repeated the girl . `` What in the world does that mean ? '' `` It means skimming along a few feet up in the air , '' answered the young inventor , who had now fully recovered from the effects of the blow given him by the midnight intruder . In spite of many inquiries , no clues to his identity had been obtained . `` How high do you go when you ` cut grass , ' as you call it ? '' asked Miss Nestor , and Tom thought he detected a note of eager curiosity in her voice .