I pressed 'e' to open my inventory while mounted on a NBT-edited horse.
What I expected to happen was the inventory to open, but the game crashed without warning.

To Reproduce:
1. Go to the world in the 'saves' folder of .minecraft and select the world that has the horse that you want to edit the stats of.
2. Open the 'player' .DAT file with NBTedit
3. Select the 'Data' drop-down, then the 'Player' drop-down, then the 'Riding' drop-down
4. Find the 'Attributes' menu, and locate both 'generic.movementSpeed' and 'horse.jumpStrength'
5. Set 'generic.movementSpeed' to "0.75"
6. Set 'horse.jumpStrength' to "0.75"
7. Save the file and close the window
8. Open and run minecraft
9. Mount the horse and the game crashes