As far as I can tell it doesn’t seem possible to one-hit-kill enemies. I had a couple of footmen with a Giant Bone Axe and a Giant Bone Mace (24 and 26 damage) and every single attack went like this:
There was the occasional missed attack, but every attack that landed went just like that.
normally goblins have 50 health 
if you want you can change this here: stonehearth\entities\monsters\goblins\goblin\goblin.json
Sure, but I still can’t make the math work. If I hit a goblin and do 26 damage, it should take 2 hearts, not 1. Every single attack for 26 damage would do one heart of damage, then 3 hearts of damage.
I might try tweaking the goblin health to see what happens.
I have noticed similar behavior. This might be down the game visually trying to show 2 updates simultaneously (in one update frame). One update for the goblin dropping below a quarter health and another for dropping below half health.
The visualization for dropping below half health should be visible, override the visualization for dropping below a quarter health in some way. Currently the quarter health drop is visible.
There are multiple causes I can think of that could attribute to this, but any of those would likely be a quick fix for the smart/talented people at Radiant.
That’s an interesting theory. I might try to test that as well.
The calculation for the heart display is off. Thanks for the help!