See the thing is, there are these alien eggs in a pool in a locked pool house. These old folks break into the pool house and swim with the eggs. Swimming with the eggs make them feel rejuvenated.
The old folks don't think too hard about what the eggs are, why they're there, or why swimming with them feels good. At one point, full of moxie, the old folks try cracking one of the eggs open.
Spoiler alert: it turns out the old folks are stealing life energy from injured aliens inside the eggs. Some of the aliens die. Soon after, the pool is closed permanently and the surviving aliens escape the planet.
This ends up being an unfortunately handy metaphor for all kinds of things, these days.