That's oil? It looks much more....chocolatey than I imagined. Always thought it'd be dark like black coffee. Shows you how much i know about things! No wonder people call it a dangerous place to work - the oil's all over the floor! Bet it's slippery.
Drilling mud is less mud and more like dirty water. Its quite dense for what it is, but very very smooth. Its a man made concoction that is constantly adjusted for specific weight per volume and viscosity, and pumped down the drill pipe while drilling. Its significantly heavier than fresh water, so a column of it in the wellbore creates what's known as hydrostatic pressure. This is the first step in well control as this physical weight of liquid keeps the formation from flowing during drilling. Drilling mud also serves the purpose of lubrication and bringing up cuttings and debris. Its great stuff. Sometimes mud engineers use a mix of diesel as well. This is known as oil-based mud and that is some nasty shit.