GM&O Cabooses

[BaltACD]

Was browsing the pictures on the Fallen Flags web site and came across several of some wood era GM&O cabooses that had a small door at the approximate window line in the middle of the car side.

Anyone have knowledge of what the GM&O used this particular 'door' for as it appears to be shorter than a man's height. I have see multitudes of cabooses but I have never seen one with a less than man size door in the car side.