It sits still, which is the first surprising thing.
Most of what lives at this scale is in a hurry — spinning, tumbling, colliding, gone. Stentor anchors itself by the tail, opens the wide end of its body into a rim of beating hairs, and waits. Water comes to it. It is blue, actually blue, from a pigment in its skin that no one has fully explained. And it is one cell. Not a colony, not a larva, not an animal too small to see. One cell, built like a trumpet, a millimetre or two of it, doing everything a body does with none of the parts a body uses.
Poke it and it flinches — bends away from whatever touched it. Poke it again and it tries something else. Keep going and it works down through a sequence of increasingly expensive answers, until at last it does the thing that costs it the most: it lets go of the floor and swims off to find somewhere better.
That ordering is the part worth sitting with. There is no brain in there to hold it.