As a kid, my mother would produce tapioca and sago puddings fairly regularly as an option for dessert and I have the sensation that I was one of the last generations to enjoy this pleasure, even if it was in their instant packet form. Very very occasionally I have seen them on restaurant menus in those new bistros that want to unearth traditional dishes and give them a trendy new twist.
Tapioca is a starch made from the cassava root, which we in South America recognise as yuca or mandioca. It is gluten and protein-free, thus fat-free. Notice that it has a pearly texture.
Sago is from the pith or spongy stem of the sago palm tree. Very similar in texture to tapioca as I recall.
Tapioca has various slang meanings including clingy and crazy and some we won’t go into here!
And lastly a joke. I am pretty useless at recalling jokes but somehow I remember this one from a Christmas cracker: How do you start a pudding race? Sago.