Xyoo 1986, hauv lub nroog Klisura nyob rau sab qab teb Bulgaria, tau tsim lub tsev khaws khoom pov thawj tshwj xeeb ntawm cov qos yaj ywm, qhov nyiam tshaj plaws ntawm cov uas yog cov tub zoo. Nws yog thaum ntawd qhov kev coj noj coj ua ntawm "Den ntawm cov qos" tau tshwm sim. Cov neeg nyob hauv nroog hais tias nws nyob ntawm lawv thaj av uas cov qos yaj ywm qab zib tau yug los, thiab lawv tshwj xeeb tshaj yog hwm cov kab lis kev cai no.
Hnub so yog ib txwm muaj, nws siv sijhawm ib xyoos ib zaug, nyob rau ib nrab ntawm lub Kaum Hli. Xyoo no, ntxiv rau qhov nthuav tawm ib txwm muaj ntawm cov qos yaj ywm ntawm cov ntawv txawv tshaj plaws, yuav muaj kev sib tw rau cov qos yaj ywm loj tshaj plaws, me tshaj thiab qab tshaj plaws ntawm kev sau qoob loo tshiab.