Let's go to Mexico.

You see? Home education takes you everywhere. One morning our eyes open and focus on a teddy bear; another hour, the snow, clumped in great heaps against the window. And today, anticipating having our hearts ripped from our bodies, atop a step pyramid in Tenochtitlan.

For that delight, we have to walk to get there.

Mostly because I am too mean to pay the extra £2.60 for the bus from Euston to the British Museum. Anyway, it's only 20 minutes, and in this free-range world of ours we can call it nourishment for our bodies as well as our minds.

You know the exhibition for Moctezuma is over. I hope you didn't hang on for a review from Grit. Anyway, don't worry. Grab hold of the exhibition guide. The exhibition itself? Dour.

I can't write about it all. I could say lots. The use of the Reading Room as an exhibition space. The tone of the exhibition. Moctezuma's place in an ordered hierarchy of the Mexica world. The supporting materials. The dead cold sacrificial stones. The eagle. Spare me, the eagle. The arrival of the Spanish. More slaughter. The sudden story switch, from one told in carved volcanic rocks, to a shiny oil on canvas. All dealings with death.

Shark, Squirrel and Tiger pause at every exhibited item, drawing and writing obsessively. I promise to buy the exhibition guide twenty-five times over, so we can go. They force me to linger. Squirrel returns to me, time and time again, Why did they do that? Why did they kill people to make the sun rise? Did they kill the children too?

Some things, I tell Squirrel, with a cuddle, I cannot explain. I cannot explain Mexica thinking. I am on the wrong side of the world. I can try with the Conquistadors. I know the story there. God, gold, glory, girls.

But in Mexica, it's all so different to how we live today. What we see here, in this world left behind, no-one is tender, no outstretched hands in love. No fat bellied women, no domestic pictures, no ordinary chores. Men are warriors, demi-gods, offerings.

Mortal women are invisible. Except one. She's a statue, female figure, kneeling. She has breasts, says the caption. I stare at her. I can't see them. She doesn't have breasts. She's different from the male because he has shoulder blades and she doesn't. Shoulder blades? Breasts? It's an easy mistake to make I guess if you are the industrious curator to the female figure c 1325 Mexica 42x19.6x26.5cm. But by this stage, and we are only in Room 2, I want her to have real, heaving, breasts. I know I'm living in this twenty-first century implant world, but still, by now, even a couple of fried eggs would be good. Because breasts mean children. And children mean love. But there just isn't any.

I don't know whether this exhibition simply chose all the stone carvings of power and hierarchy and eagle bone, and hid all the statues of beautiful women with breasts and plump thighs, or whether the Spanish so truly destroyed any remnants of softness, that now there really aren't representations of women in Mexica culture that are not all clawed hands and bared teeth.

So we're left with Coatlicue, who hangs dismembered hands around her neck and chills my soul with her fangs and lethal stare. Or the moon goddess, Coyolxauhqui, lying dismembered, a skull under her arm.

But there must have been mortal women; women giving birth, nursing babies, shaping the land, picking corn, working cloth, smoothing garments, pressing their hands against the scrap of life in a child. Here, nothing like that. Nothing at all.

Now I could come over all feminist and say that this strikes me as a supreme example of a patriarchal society. What is it with you boys? Military conquest, sharp spears, ripped up hearts, bloodletting, war, death and corpses.

Yet it tells me other things too, like the supreme power of any ideology. Women, giving up their children, sons, brothers, husbands, ushering them on to sacrifice, because this is Wednesday, and this is how devotion is shown. Did those hands willingly guide those kin farewell on the journey to feed the sun?

Did no one say, let's not do that? asks Squirrel. Let's give the sacrifice a miss, just for today? Let's play music, and see what happens instead, tomorrow, at dawn?

I draw Squirrel close, and tell her that ideology means sometimes people do things that it's not in their best interest to do. And while individuals might question the vision, they can rarely break free alone; they need the support of many. And if we're taking home a lesson, it could be that one.

Or perhaps that we should all draw more pictures to leave behind us. Pictures of fat women and men enfolding children and laughing with love.