Good observations! Soma was indeed shot in the hand.
Agni’s eye was slashed:
I think this was to play off the fact that Prince Soma and Agni were the perfect foils for Ciel and Sebastian. They were another master and butler duo, yet they were almost exact opposites. Soma was trusting, naive, warm, and caring, while Ciel is unable to trust, is bitter, cold, and selfish. Agni was a genuine, kind, humble person, and Sebastian is an egotistical demon who is simply playing a part until he is able to eat Ciel’s soul.
Since they were such opposite mirror images of each other, I wonder if what happened with Soma and Agni is any foreshadowing to what might happen with Ciel and Agni. Only time will tell.
Thanks so much for writing!