Just riffing on the ideas here..

What if the mask making behaviour was an example of interspecies psychic buological emergence?

Emergence (from a biological perspective) is when small seemingly unconnected entities instinctively behave in a way that reveals a larger cohesive pattern or system. For example, does the individual ant know that it is contributing to the efficient functioning of a hive? Do birds understand the intricate physics behind their flight formations with other birds? No. They just do it somehow. A bit Ike in the video: https://laughingsquid.com/fish-surround-diver-in-a-bait-ball/

The fleas are somehow creating an emergent representation of themselves through their interaction with the humans.

For the purposes of protecting their hosts from dying, and therefore maintaining their food source.

Okay totally made up, but fun to think about regardless!