I can do the same. Not only with pots but tile as well or if there is a hollow under a tile.

So you're saying it is not a skill? (LOL)

Oh it's a skill, only found with people who pay attention or where trained. In my case I was trained by grandfather who was a tile setter for fifty years. I would bet you pay attention to your plants and pick it up that way. My grandfather had a contract with a mall to fix and maintenance the tile. He would have me crawling around taping on tile with a lighter looking for the ones that didn't sound right and marking it with chalk. After a while I could tell by the sounds of people walking around and would be able to sit and listen as people walked by and find them. Now it's second nature.

Bricks too...the bad bricks make a different sound when lightly tapped together. And any glazed pottery...a glazed pot should ring when the rim is thunked with finger nail but when the tone stops short there is a flaw in it. And as for the tile with a hollow...roll a golf ball across your floor, you'll find them...i have one hollow tile in the path thru the dining room.

And then there is thunk of a good watermelon...i swear it must be a lost art to hear a good melon cause people look at me odd as i am knocking the melons with my knuckle but i very rarely get a bad melon...tho sometimes those that have been dropped and cracked inside will thunk like a ripe melon, i am trying to train my ear to hear that flaw but it happens so rarely its hard to train an ear to a sound it very rarely hears.

Pea, I was tapping watermelons the other day and some guy said "That doesn't work, you know." I just smiled and kept on thumping them.