"Forced rhubarb" is rhubarb grown to maturity in complete darkness -- during which it grows so rapidly it produces incredibly cool, weird sounds.
If you listen to that video above you'll get an earful: Rapidfire clicks and pops that sound like somebody irregularly whacking a couple of wet sticks together.
The process of "forced rhubarb" -- a term I am using for my next band name obviously -- is outlined nicely in this story on Atlas Obscura:
The method of growing forced rhubarb dates back to the early 1800s, and continues in much the same way today. Farmers let the rhubarb grow out in the open for two years, as the roots collect and store calories. Then the plants are transplanted to lightless growing sheds around November, where they continue to grow—warm, but out of season and in the dark. The rhubarb grows without photosynthesis, which normally makes the plant tough and fibrous. “You get a lot more tender, less tart rhubarb. There’s not too many strings. Outside rhubarb is quite stringy. When you’re cooking with [forced rhubarb] you use around 40 percent less sugar,” says French. The process also results in deep, red stalks, without the normal green shading.
As the stalks burst up out of their initial buds, they create a distinct popping sound, and as they get larger, the stalks rub together and create squeaks and creaks. “It’s growing over an inch a day. It’s not like your field or garden where things are growing two to three feet apart,” says French. “Every root is right tight to one another.”
(CC-licensed photo above from Timothy Vollmer)