Is it true that pudding is thickened by egg yolks?

Yes, it's true that many types of pudding, particularly custard-based varieties, are thickened by egg yolks. The proteins in the egg yolks coagulate when heated, which helps to create a smooth, creamy texture. However, not all puddings use egg yolks; some are thickened with cornstarch or other thickeners instead.