"That's all, gentlemen... except to say that Agnew might have jumped that rock wall, under Mars' low surface gravity and the impetus of fear - but I could not and I tried - and to mention that these two crewmen were wearing breathing gear - have to, on Mars - and hypoxia can make a man's senses quite unreliable.  I don't know that the first crewman was drunk through oxygen shortage; I just mention it because it is an explanation easier to believe than what he reported... which is that Agnew simply disappeared in the blink of an eye.  In fact I suggested as much to him and ordered him to check the demand valve and the rest of his breather gear before he went outside again.