> But you also have a similar thing for Carnival: Traditionally, it's the last feast before Lent (where Lent is also an expanded narrative of Easter!).

So Lent is not an "expanded narrative of Easter"; it's a period of preparation, prayer, self-denial and almsgiving; it represents the 40 years' wandering in the wilderness that the Jews endured, and the 40 days in the desert when Christ was tempted by Satan. So it's distinct from the Easter celebrations.

Carnival is not a "Christian feast". Carnival is an umbrella term for various secular celebrations. But indeed, this has roots in Jewish traditions.

What the Jews will typically do in preparation for Pesach is to cleanse the home of all forbidden leavening and unkosher food: chametz. And this is sometimes done in a quite ritualistic fashion, and the children are involved, and it's like a scavenger hunt (and may have some cultural exchange with Easter Egg hunts) where the adults may challenge the kids to find every crumb of chametz and collect it and present it to the head of household. Then the chametz is destroyed, or sold or traded to a Gentile.

And so Carnival (folk etymology may consist of "farewell to meat [carne, vale]") is a festival where people are eating up the leftover meat that they've stored up. "Mardi Gras", "Fat Tuesday", and "Pancake Tuesday" is where they're using up the remaining fat to make pancakes. The Byzantines have elaborate fasting/abstinence rules which preclude the use of oils and butter and many things for certain periods. And this reflects prior Western traditions. Abstinence from meat used to stretch for all of Lent, not just Fridays. And so, Carnival was one of those cycles where you prepared for Lent (itself a preparation) because Lent was going to be the "lean months" before the springtime feasting.

And of course Carnival also took on the carousing and drinking and licentiousness of fertility rites; why not all that. If you were eating meat then you probably had some good wines or booze to go with it?

But Carnival has never been a Christian sort of religious or liturgical feast or season. Carnival coincides with Ordinary Time these days, or "Sundays after Epiphany" in the old General Roman Calendar of 1960. But Church authorities and Canon Law did not specify any particular methods for eating up our stores of flesh meat, or getting it on and flashing boobs on Bourbon Street.