Flashing Minnows?

[Knife]

I have four rosy minnows, along with four Albino corydoras; I've noticed over the past few days that my biggest minnow, about 1.5 inches has been flashing against the sand. I first suspected Ich, and has been closely watching them, but I haven't seen any white spots or noticed any other symptoms.
And it's only the one big one that flashes, and they all look healthy as far as I can see.