A normal, modern piano has three little feet, more commonly called “pedals”:
On a grand piano, the right-most one is called the damper pedal, the left-most one the una corda, and the middle one the sostenuto. When depressed, the damper pedal lifts all the dampers off of the strings. The una corda pedal shifts the hammers over so that they either strike fewer strings or strike the strings with a mushier part of the hammer, either way creating a softer sound with a slightly different timbre. The sostenuto pedal is depressed after some keys are held down on the keyboard, keeping the dampers on those notes raised so that the hands can be free to go on to other things in life. On an upright, the middle pedal is often a so-called practice pedal that lowers a piece of felt between the hammers and strings to severely dampen the sound, and the una corda is replaced by a half-blow pedal that achieves a softer sound by pushing the hammers closer to the strings.
None of that information is as important to know as this one: do not stomp on the poor piano’s pedals! Just as anyone who purposely stomps on your foot is an annoying, hateful person, anyone who stomps on a piano’s pedals is an annoying, hateful person. Pedals are possibly the finickiest part of the piano for a piano tuner to regulate. Practically every piano I’ve played has at least a few notes for which the sostenuto pedal doesn’t work. Dampers often don’t raise evenly across the strings, damping notes inconsistently, or causing some fuzzy bits to scratch the strings while the damper pedal is being raised…
Which leads to my pet peeve. A lot of student composers seem to think that stomping on the damper pedal is a great and unique effect (every student seems to think this at some point in their life) since unregulated dampers can cause some echoey piano sound when the dampers are raised quickly. First, notice how the pedals are attached to the main body of the piano by a few screws. They are actually quite delicate. Some heavy stomping could bend the metal bars the pedals are suspended from, as well as knock the pedal action out of alignment. Second, the effect caused by damper-pedal-stomping differs from piano to piano. A well-regulated (i.e. healthy, harmless, innocent piano) will barely make a sound when its damper pedal is depressed normally. This does not mean that stomping on the pedal will make a bigger sound! Instead, it means stomping is not the solution.
Any sane composer who wants an echoey effect from the piano should know that there are many different options available. All of them require that the damper pedal is depressed (without stomping, of course.) Once that step is achieved, an echo can be obtained by hitting a part of the piano that will not cause harm, such as the frame (as mentioned in the previous Exploring the Piano post) or a support bar inside the piano, or the strings (not the dampers!) An ingenious composer could also run a sheet of paper over the strings, or a sheet of plastic, or speaking/whispering into the piano. More on things you can do inside a piano later.
If you ever need to keep the damper pedal down for a long period of time, say, for walking around the piano and doing things on the other side of the frame, one simple solution is to put a rubber wedge under the pedal at its back. Notice that there would be a bit of room under the pedal if it was depressed.
I’ve noticed that this part isn’t accessible on Bösendorfer pianos, so you would have to find another option, such as getting your page-turner to hold down the pedal for you.