Black hole (or BH) is a Liquid Webtoy tool.
Black hole is activated by left clicking and holding on the playing field. It sucks in all elements and objects (except wall) from around the playing field and destroys them, as long as the black hole remains activated. In Liquid Webtoy, BH comes with a scale which goes from 1 to 5. The higher the number, the faster it sucks in elements. In Liquid Apptoy, the scale does not exist, and BH strength depends on the size number.