Not only carp but .....
There are lots of species amongst our scaled friends who seem to 'shut down' after one or two fish have been taken from a pod. Smallmouths, Mutton and Mongrove Snappers, Mahi Mahi and Barracuda come immediately to mind - not always but frequently enough for it to be the rule rather than the exception.
The main exception here was fishing dries to the smallies which they seemed happy to rise to all night!
I've read about the Carp secretion also. I was wondering if there was also some kind internal effect - maybe a hormone release surpressing the "attack" response. I conducted a samll experiment on a couple of pods of smallmouths last week-end.
On first seeing the fly the fish go crazy for it and there's a lot of competitive presure and its hard to miss a strike. Next time through, the interest seems to drop by about 50%. After a couple more presentations you can almost bop the fish on the nose and they'll ignore it. Not scientific by any means but interesting.
When sight fishing, look over your shoulder from time to time, you never know who's behind you