  Gompf showed that for $K$ in a certain family of double-twist knots, the
swallow-follow operation makes $1/n$-surgery on $K \# -K$ into a cork boundary.
We derive a general Floer-theoretic condition on $K$ under which this is the
case. Our formalism allows us to produce many further examples of corks,
partially answering a question of Gompf. Unlike Gompf's method, our proof does
not rely on any closed 4-manifold invariants or effective embeddings, and also
generalizes to other diffeomorphisms.
