虎口

tiger's den / dangerous place / the web between the thumb and forefinger of a hand

tiger / CL:隻|只[zhi1]

mouth / classifier for things with mouths (people, domestic animals, cannons, wells etc) / classifier for bites or mouthfuls

lit. to escape from the tiger's mouth (idiom) / fig. to narrowly escape death

lit. a lamb in a tiger's den (idiom) / fig. to tread dangerous ground