Excuses can be invented. Hitting a deer somewhere is different from hitting a deer at a point that kills it almost instantly, and hitting a rabbit at one distance may be much easier than hitting a deer at a much greater distance. Still, it seems that the mangaka was essentially thoughtless, and simply treated the killing of a large, strong animal as more challenging than killing a small, weak animal, as if the killing were bare-handed &c.Hitting a rabbit is way more impressive than hitting a deer, imo.