In that case - never shoot a deer again as the bullet can change direction drastically, exit the animal and hit “surfaces they shouldn’t be sent into”.....and plenty of bullets carry enough energy after hitting a target to kill.
standing at the bottom of a hill shooting at something halfway up it may result in a ricochet...but the risk must be assessed, the chances of the ricochet doing damage and passing the side of the hill is minimal and so as low as reasonably practical.
I’d love to know how all the folks using night vision/thermal are clarifying there isn’t a stone or hard ground behind....the answer is they are not - but they most likely know the ground and the backdrop and the risk is usually low.
regards,
Gixer