The answer is in the image attached.
Hope this helps!
Bacteria are classified into five groups according to their basic shapes: spherical (cocci), rod (bacilli), spiral (spirilla), comma (vibrios) or corkscrew (spirochaetes). They can exist as single cells, in pairs, chains or clusters. Bacteria are found in every habitat on Earth: soil, rock, oceans and even arctic snow.
It's empty or fairly large, making the sounds from your hands bounce of the walls and therefore having it echo
