‘Decapitation’ is the act of removing a head from the body.
The word you are looking for is ‘dedigitation’. This is the act of removing one or more fingers.
For a second I got my Latin really mangled and thought the correct word was ‘defenestration’ which actually is the act of throwing a person from a window. Which doesn’t make sense at all. You are not removing the windows from the person but removing the person from the window. No wonder Latin died.
But still…you meant to say ‘dedigitation’. In case you were wondering I’m just making a deal about this because you went on and on about how people who don’t believe in evolution are stupid. The way you said it was rude. So I just feel like pointing out the fact that you don’t know every blessed little thing.