Concepts of thermalization and hydrodynamical behavior are applied from time to time to e + + e − , hadron+hadron and heavy ion collisions. These applications are scrutinized paying attention to particle multiplicities, spectra, and Bose-Einstein correlations in particular. Can hydrodynamics describe these data? * e-mail: csorgo@rmki.kfki.hu 1 Instead of the originally given e − +p problem, let me discuss soft hadron-proton collisions, for clarity.