One puts length through headless vampire, twitching (7)

'one' is the definition.
I don't know anything about this answer so I cannot tell whether this works.

'length through headless vampire twitching' is the wordplay.
'length' becomes 'l' (abbreviation in geometry).
'through' is an insertion indicator (inserted letters go through the word).
'headless' means to remove the first letter.
'twitching' indicates an anagram (letters twitch or move into a new order).
'vampire' with its first letter removed is 'ampire'.
'ampire' with letters rearranged gives 'impaer'.
'l' inserted into 'impaer' is 'IMPALER'.

'puts' is the link.

Can you help me to learn more?