Original: Mandelstam's non-conformist, anti-establishment tendencies were not heavily disguised, and in the autumn of 1933, they broke through in form of the famous "Stalin Epigram".
Simplified: Mandelstam's non-conformist, anti-establishment tendencies always simmered not far from the surface, and in the autumn of 1933 they broke through in form of the famous "Stalin Epigram".