Á tử ngặt hoàng liên.

A mute keeping goldthread in one’s mouth.

The meaning is being unable to speak despite the pain and discomfort (i.e., bitterness). Goldthread is a bitter herb used as medicine. This is similar to “Holding one’s tongue” or “Cat got your tongue?”

Ăn như gấu ăn trăng.

Eat like a bear eating the moon.

The meaning is criticizing people who eat greedily and quickly. In the past, lunar eclipses were believed to be Asiatic black bears (aka moon bears due to the white crescent shaped patch of fur) eating the moon very greedily and quickly. This is equivalent to “Eating like a pig.”