I didn't know that some birds hang upside down 并列题名：I didn't know that some birds hang upside down I didn't know that some bugs glow in the dark 并列题名：I didn't know that some bugs glow in the dark I didn't know that crocodiles yawn to keep cool I didn't know that chimps use tools I didn't know that dinosaurs laid eggs I didn't know that whales can sing I didn't know what time it was 并列题名：I didn't know that crocodiles yawn to keep cool