I'm not sure if it's still the case, but I remember a few years ago how commercials would get shorter over time. Take a single commercial, and start off showing all N seconds of it. Then, later, just show a brief section of it, and let the person's brain do the rest.

That, and I've read somewhere that people tend to remember the beginning and the end, but not the middle for a given thing. Edit the end because that's what people will remember, but it also won't stand out as being fully edited.