The invention relates to a rubber teat element (1) having a head part (2) and a shank part (3), which is connected to the head part (2). The head part (2) has a lateral surface (5) and an introduction opening (6) for an animal's teat, wherein the introduction opening (6) is delimited by an inwardly oriented lip (4). The lateral surface (5) has at least one expansion region (7), which extends over at least part of a lateral-surface circumference (8) and at least part of a head-part length (9), wherein the lateral surface (5) is of undulating form, as seen in cross section, in the expansion region (7). The invention also relates to a teat cup and a milking cluster having a corresponding rubber teat element. The present invention provides a rubber teat element which, in particular in the case of small, thin and short animal teats, can be adapted to different teat geometries on account of the radial expansion capability of the head part.