The yapping puppies

Julia liked to buy wind-up toy dogs and release them in the hallways at work.
They’d yap for a few minutes before winding down.
When someone made a battery-powered yapping dog, she bought a bunch of those and released them in the hallways.
They’d yap for thirty minutes before running out of power.
Someone suggested to Julia that actual puppies would yap for a lot longer.
So, she went to the pound and got a bunch of those.
She set them out late Friday night so they’d surprise people on Monday morning.
But she didn’t leave out food or water.