In Hanna (2019), Episode 2 (maybe 3?), Erik buys 2 kilos of goose fat and then rubs it on himself before swimming across the lake. What was the purpose of this?
He swam either the Oder river or the Szczecin Lagoon to get from Poland to Germany. Not exactly sure why since Poland is in the EU Schengen area and there are no border checks.
Cold water and ocean swimmers will often put fat or Vaseline on their bodies to help retain heat, reduce chaffing from swimsuits, help prevent salt burn, and help them through the water. Consider it a natural form of a wetsuit.
Spoiler: Perhaps what he did after meeting the police officers on the other side was why he swam the border rather than just walking across it.