Beck vs. beckon
Right: She’s at your beck and call.
Wrong: She’s at your beckon call.
What the idiom means: She’ll be on hand to help you whenever you need it!
Chalk vs. chock
Right: Chalk it up to the good weather.
Wrong: Chock it up to the good weather.
What the idiom means: Chalk it up means crediting something with a reason.
Think vs. thing
Right: You’ve got another think coming!
Wrong: You’ve got another thing coming!
What the idiom means: Watch out—if you think this is the result of your action, think again!