@RapidLord
Not Sounds, vibrations. And in normal situation ... it wouldn't work, however the cage in the center of the panopticon is made as a single structure. Both tables are bolted down to it.
Which ... makes sense if its used to interrogate people. You don't want them to be able to fight back by flipping the table right ?
Now here is the question, what material is the table made off ? Tables are often made of wood however it wouldn't be good with water since the rooms are made to torture the prisoners by immersing them in water. Plastic is another option, but wouldn't fit. My thinking is that the table is made of the same material as the rest of the structure.
In chapter 433 page 8 during the first round, Baku tapped on the table.
There is 2 options as to why he could be doing that, first to check what the table is made off. Second, could he use tapping as a way to communicate.
Now let's think, if the table is made of metal and Baku used the corner of the cards to carve on it, in normal situation it would make some serious noise. However carving on metal would also generate a lot of vibration that could easily go from the table to the rest of the cage. Think of it as scrapping the side of a car with keys, it doesnt require much force, but would make lot of noise. Here, replace noise by vibration through the metal.