Night Hunting

The museum of a university lost several boxes of butterfly specimen, then a night watcher was hired to guard the museum in night. One specimen each of polar bear and gorilla were added to the museum. About two weeks after the specimen were left at the corner of an exhibition room as they did not have appropriate cabinets to put them in, the specimen of polar bear was missing together with an ancient dagger. The window was bolted inside and the door was locked normally and securely of the exhibition room. There was no trace left in the room. The night watcher reported: four to five days after the specimen were put in the exhibition room, in one morning he noticed the position of the bear changed to another position; one week before the bear was missing, he heard feet stamping sounds, noticed the bear was caressing and slapping the gorilla through a keyhole of the exhibition room; in the night when the bear was missing, the night watcher said the museum was as quiet as a graveyard and he did not hear any abnormal sound. Next day after the bear was missing, someone noticed there was an irregular circle of footprints of the bear on the smooth muddy ground under the window sill of the exhibition room; a patrol policeman said he noticed a white thing with an opened mouth, was hit at the back of his head and fainted to ground near the university. A lot of newspapers reported about the incident with pictures of the museum and the gorilla specimen. Several days later a gambler met the bear outside of an underground casino, fainted due to fright, when he woke up, he found he had already lost his valuables. What really happened? How could the specimen of the bear act in such weird fashion?...