Note nothing regarding blood (4)
I believe the answer is:
gore
'blood' is the definition.
('gore' can be a synonym of 'blood')
'note nothing regarding' is the wordplay.
'note' becomes 'g' (musical note**).
'nothing' becomes 'o' (looks like zero - 0).
'regarding' becomes 're'.
'g'+'o'+'re'='GORE'
(Other definitions for gore that I've seen before include "Bloodshed" , "Blood that's been shed" , "Poetic blood from Al?" , "Pierce or wound with a horn or tusk" , "Clotted blood" .)