(with thanks to M.H. Forsyth)
Why Thomas opened that door, we may never know. It could have been something he did instinctively, some remnant of an ancient primal urge. It could have been an impulse from the depths of his brain, a half-remembered childhood memory tugging gently at his conscious mind. It could have been something he had been planning for weeks, knowing long before now that he would open the mysterious door at the first available opportunity. It could be that he was not human at all, with none of the caution and instinct for self-preservation humanity brought, but a sophisticated android with a pre-programmed agenda for door-opening. There really is no way of knowing without some kind of detailed neural scan.
Maybe his name wasn’t even Thomas. After all, guessing someone’s name based on their appearance is often a matter of pure chance. Suffice it to say, there was a human, or humanoid figure of some sort, opening (or appearing to open – such tricks of perception are possible) something that looked very much like a door, but don’t hold me to that.