“A transition between two shots during which the first image gradually disappears while the second image gradually appears; for a moment the two images blend in superimposition. Dissolves can be used as a fairly straightforward editing device to link any two scenes, or in more creative ways, for instance to suggest hallucinatory states.”

– Yale Film Analysis Course

“Psycho” (end of shower scene), Alfred Hitchcock. Dissolve from the drain to Janet Leigh’s dead eye [Click to watch]