Hang on to (someone or something) like grim death British verb phrase
To grip, grasp or hold someone or something tightly because you do not want to lose it or fall
As soon as the branch broke off, I hung on to another branch like grim death.
The verb "hang" should be conjugated according to its tense.
Used to imply that someone is acting as if he or she is demure, innocent, sincere or reserved but they may be not
Don’t be fooled by Jennie's good behaviour. She looked as if butter wouldn't melt in her mouth.