Jamieson, Fausset and Brown on Genesis 40:18-19

18-19. Joseph answered and said, This is the interpretation--The purport was that in three days his execution should be ordered. The language of Joseph describes minutely one form of capital punishment that prevailed in Egypt; namely, that the criminal was decapitated and then his headless body gibbeted on a tree by the highway till it was gradually devoured by the ravenous birds.