In British private schools children shout "Quis?" and the person to shout "Ego!" in reply first gets whatever was on offer. The Latin derivation is clear but I have two questions.
First, when did this practice start?
Second, there is an extension where the respondent shouts something that sounds similar to "ego de to my liking". This means that the child will accept the gift if they like it. This is to prevent the first child from giving a rotten egg or black eye or similar. When did this first appear?