I don't think anti-aliasing is the explanation. I had a look at the GIF zoomed up in Paint.NET and there's nothing unusual about it, just the gray triangle with

I don't think anti-aliasing is the explanation. I had a look at the GIF zoomed up in Paint.NET and there's nothing unusual about it, just the gray triangle with some lighter-shade pixels around the edges. I think the browser has a flaw when enlarging images with transparency - eliminating the transparency around the arrow would probably fix everything.