He climbs to the top of the glass, spreads himself out, and floats around upside-down on the surface. A tetra bumped him, and he curled up and sank to the bottom, so he definitely wasn't stuck up there. The second he hit the substrate he went right back to the glass and did it again.
Why? Whats his deal? We have a handful of assassins and none of the other ones are doing this. He only does it when the light is on.
Thanks! I've got one of those "natural sunlight" lights with multicoloured LEDs. The plants love it and it looks awesome. Also it apparently hypnotizes snails