If there were any sense in the world this would be a repeated klaxon with Lance Corporal Jones [1] shouting "Don't panic! Don't panic!"
[1], for left-ponders, https://en.wikipedia.org/wiki/Lance_Corporal_Jones
[1], for left-ponders, https://en.wikipedia.org/wiki/Lance_Corporal_Jones
So in this instance, left-ponders would be Americans to someone in the UK, and right-ponders would be English to someone in the USA.
"I ordered lunch for my parents as they spent too long pondering over the menu and wouldn't make a decision."
Quick edit : I've heard of "over the pond" to mean the other side of the Atlantic, but never heard the phrase "left ponder" at all, let alone to refer to Americans.