> Also: it's a one lane road and "over taking" is not possible.

I've eaten some hamburgers at Krystal's that definitely overtook whatever else was in front. Some folks have had the same or similar effect from White Castle, although I never have. Chipotle on occasion moves things along rather briskly too. No fruit or green leaves in any of them.

It may be that it's not a digestion thing, but some other factor they have that accelerates the process.

Not a doctor but I know that some foods, in some guts, at some times can trigger a 'quick-release valve' of sorts. You're not digesting properly when that happens.