It's sold in a carton that looks like milk, and the packaging itself tells you to shake it — the sorghum and maize sediment settles to the bottom and has to be mixed back in before every sip.
Chibuku is a commercial version of traditional Botswana sorghum beer (bojalwa), a thick, sourish, low-alcohol brew made from malted sorghum and maize. It's sold cheaply in waxed cartons or plastic bottles from bottle stores and shebeens across Botswana, shaken to redistribute the grainy sediment before drinking.