The horrible tangled mass of hair, soap scum and bodily fluids that clogs the plughole of a bath or shower.
Usually caused by women who wash their hair, shave their legs and armpits or trim their pubic hair in the shower.
If not dealt with in their early stages, they will grow, block the pipes, float around in a pool of water that spills onto the bathroom floor. and produce a clan of sentient offspring that attack you in the dead of night and drag you off into the sewers.
It takes a brave man to remove a bathroom wookiee.