Terminator 2 Thumbs Up
When Ryuko, Mako and Maiko are running across the pot full of lava in episode 4, if you're quick enough you can see the skeletal arm of The Terminator from Terminator 2.
In episode 4 of Kill La Kill when Ryuko, Mako and Maiko are running across the pot full of lava, we see there are many bones inside floating on the surface. One of those bones is none other than that of The Terminator, or more specifically, his hand at the end of Terminator 2.
The easter egg is made more apparent once you pause and zoom in as you’re then able to see it’s not just a floating hand, but that the hand is making a thumbs up, exactly the same as in Terminator 2.