Vampires do this part with sweetheart (4)
I believe the answer is:
bite
'vampires do this part with sweetheart' is the definition.
'bite' can be an answer for 'part' (thesaurus). I am unsure of the rest of the definition.
'part with sweetheart' is the wordplay.
'part' becomes 'bit' (both mean a piece of something).
'with' says to put letters next to each other.
'sweetheart' becomes 'e' (the heart/centre of 'sweet').
'bit'+'e'='BITE'
Can you help me to learn more?
(Other definitions for bite that I've seen before include "Nip; nibble" , "power" , "Mouthful" , "Cut with the teeth" , "Punch" .)