Revealing mistake: When Chang is getting blasted with the minigun, the safety pads under his shirt are very noticeable. (His shirt is extremely "puffed out" and you can see the outline of pads.) He's been tied up most of the episode and wasn't wearing pads earlier, so there's no way he was able to get pads on in the meantime.
Revealing mistake: When Chang's paint bomb explodes, pay attention to the background. You will see paint exploding from three different points on the ground. (One to the center, one to the left and one to the right) The only problem is that there was only one paint bomb in the center, so it makes no sense that there are 3 explosions from different points.