What is the first horrifying sight that Elie sees and disbelieves in Night?

In exploring this question, I thought that Wiesel's description of Elie's travelling to the camp might constitute as a horror that warrants a sense of disbelief.  The cramped conditions, as well as the open sense of flirting in the midst of this horrendous moment, and the notion of the destination might qualify as potential areas where disbelief could enter.  In analyzing how Eliezer details this voyage, one can see that there are moments where doubt, pain, and fear all converge within the narrative. These elements could be seen as the first moments where the nature of the Holocaust could have revealed themselves to Elie.  In reading the descriptions, there seems to be an undercurrent of disbelief within the narrative structure.  This might be due to the fact that Eliezer himself is unaware of what is going to happen, yet his mind begins to enter the domain of understanding that there will be little in way of both positive ending and escape from such a condition.