Plasma weapons
The science nerd in me is bugged out that aliens use plasma weapons and are able to shoot matter, that has lower densities than in gas state and are literally so energized that the bonding forces between protons/neutrons and electrons start to "fail".
But halo at least not just turned plasma weapons into high energy weapons that are makeshift laser weapons like in star wars, instead they give those "projectiles" at least a gassy nature and make the big ones slow, like the turrets, wraiths and charged up plasma pistols.
Is there any explanation given how the covenant manages to shoot plasma?