“Heavy going”

“When pigs fly”

Something that will never happen.

“Kill two birds with one stone”

To achieve two goals with one action.

“Raining cats and dogs”

Raining very heavily.

“A picture is worth a thousand words”

An image can express more than words.

“Wrap one's head around something”

To understand something complicated.

“Catch someone red-handed”

To catch someone in the act of doing something wrong.

“Every cloud has a silver lining”

There is something good in every bad situation.

“Put your money where your mouth is”

To support your words with actions.