Do you ever hear the expression “That’s the last straw”? Or do you know someone following a problem who wants to know whether “That’s the straw that breaks the camel’s back”? What if they’re the same straw?

I want to collect pairs or sets of expressions like that. I’ve been on the lookout for them since I found some British writers who expressed skepticism by writing “Pull the other leg, it’s got bells on!” instead of just saying “You’re pulling my leg.” Sometimes it was “Go on, pull the other one.”

Sometimes I wonder if it’s a regional thing, like whether you call your carbonated beverages pop, soda, or fizz. (Personally, if I say yes to a soda, fair warning — I will expect ice cream.)

Other times, I think it must be involved with our national senses of humor, or at least of what phrases are funny. Some of my favorite memories of watching TV with my parents involved the British comedy “As Time Goes By,” in which Geoffrey Palmer and Judi Dench portrayed a couple in love — after a gap of 38 years when they didn’t see each other.

Instead of saying that he’d do something “When pigs fly!,” Lionel Hardcastle (Palmer) stopped in an argument with Jean Pargeter (Dench) to say “What was that?”

Jean could only ask “What was what?”

“I thought I saw a pig fly past the window,” Lionel replied. That’s so much fresher than just saying “When pigs fly,” and it has the added advantage of confusing an opponent.

Feel free to add your own questions or suggestions as comments. We’ll see what matches up.