At the start of PART II, when they are dragging the Irish boy out of the water, you can hear Newt, or maybe Jasper say "Watch your horse, Danny, watch your horse"...not Deets as was his character name.
After watching this scene over a dozen times & with a headset so there could be no noise intrusion I never heard the word "Danny" or "Dan" at any time. I disagree completely about this slip-up
After watching and listening to the scene, I was able to distinctively hear someone say "Watch your horse Danny" It appears the horse was getting close to stepping down on the person laying down in the water. It could have been Jasper or perhaps a horse handler off to the side of the shot.