"Knock on wood" nghĩa là gì?

Ví dụ

I haven't had a cold all winter, knock on wood.

It was one of those moments that in hindsight Lake Charles Mayor Nic Hunter wishes he would have knocked on wood and spit three times as he said on Aug. 19: “We’ll be in decent in shape unless a hurricane hits us.”

After several rounds of tests, followed by some pretty good medications, I was sent home with a strange plastic bottle and a tiny strainer, neither of which I ever used. And 187 bottles of Gatorade later, I must have passed the stone as the pain went away and was not present on the ultrasound (siêu âm), which I had the following week. Knock on wood, a year later, no more signs of kidney stones (sỏi thận).