Just making sure my pond snails hang out on the rim of my tank and sometimes they fall off and sink. If they get spotted by a rasbora while falling they get eatenInteresting question.
Let's analyze this.
1). Looking at my school of harlequin Rasboras and comparing their mouth's size to my ramshorn snail's I would have to say that any ramshorn snail that fits in their mouth would have to be tiny in size. I mean, my harlequins cannot even swallow an entire Vibra Bites without spitting it out, several times, and still can only eat about half of it.
2) IME Harlequin Rasboras tend to mostly inhabit the upper half of the tank, they only "go for" food that sinks below the surface and floats down to mid levels of the aquarium. But rarely do they dive down to the lower 3rd of the water column, or feed directly off the glass or surface, where snail's spend most of their time. Snail's mostly live on substrate, tank glass, plants and decor, and on plants that float at the surface.
So hypothetically, IMHO, if a snail just happens to sail by a harlequin Rasbora and the rasbora attempts to eat it and the snail is able to fit in the mouth of a harlequin rasbora and the fish is in fact "able to" swallow it whole, then I would not worry about it....