One only gets rebound in the nose, but I'll probalby screw it up trying to explain why. (Let me run downstairs real quick and ask the live-in doctor.) (OK, I'm back...) It has to do with the differences in the mucosa. The one of the nose is more mucous producing while that under the tongue is not. When a chemical is sprayed in the nose, it acts as an irritant which stimulates mucous production. Not so sublingually. Both areas have a good blood supply, which is needed to get the syntocinon into circulation--so why not avoid rebound if it is someone using the spray several times a day. (And not everyone does.) Oh yeah--my husband said it could be sprayed into any body opening having a good blood supply--I won't mention the example he cited. Karen