So, yeah, for a while, when I've hit any mob (be it a cow or a creeper), they emit heart particles instead of the standard hit particles. No resource pack, and although I am using shaders in the picture, the problem's been troubling me for many months, before I started using shaders. Only been on this computer though. I can't even honestly remember when it started.
I seem to remember the hit particle being some form of a cross, but on the off-chance this is the default (which I can't seem to find), that's fine.