Mismatched monster model

I was making a house in the swamp when weirdly,on a dark and stormy night (no joke,it was dark and stormy) I saw this:
A zombie with no arms and a slime skin.His head was that green with the eyes on the side,no mouth, and there was nothing at the arm area.Bug or something else?I tried to get a screenshot,but I forgot how to on a Macintosh.