Moses is referring to an event in the past when Dathan and Abiram rebelled against Moses and Aaron. The full meaning of this statement can be made explicit. (See: [[rc://en/ta/man/jit/figs-explicit]])
Yahweh causing the land to split open so that the people fell in is spoken of as if the land had a mouth and the ability to swallow people. (See: [[rc://en/ta/man/jit/figs-personification]])