Glow squids would fly out of their cages if the cages had no corners and axolotls were nearby. This effect is amplified when more axolotls are around, as seen using a cage with more axolotls. The image below called "This is the smallest setup possible" shows the smallest setup possible to get the glitch working without a glow squid dying.

I was testing and found out that this is not a visual bug, since I can hit a glow squid even when it has flown out of the wall.

How to reproduce:

1. Build a cage. (or two)
2. Fill a cage with axolotls.
3. Fill the same or the other cage with glow squids.

If you're wondering how the axolotl is smiling, I used the Vanilla Tweaks resource pack.

Or build this: