An enraged gorilla terrorised zoo visitors after the beast charged around its enclosure before shattering its glass walls. Onlookers at the San Fransisco zoo recoiled in terror as 400-pound Denny threatened to break free from his pen on Saturday 11 October. Families dispersed as ten-year-old Denny hurled himself full force at the glass. "It literally felt like an earthquake before we realized that that was just him hitting the glass," visitor Jackie Doubler told 10News . "It was pretty scary.