What does the cryptic crossword clue "Impale vampires as they sleep? (4)" mean?

The definition is "Impale". The wordplay uses a reversal. BATS (reversal="for example vampire bats") = STAB; definition: "Impale" The answer is STAB.

Impale vampires as they sleep? (4)

Independent Cryptic #11377 | 24 Down | 2023-03-30 flower