|Abstract:||There are two mysterious gaps in Tianjin ditonal sandhi that have hitherto not received the attention they deserve. With two tonal features [high] and [low], Tianjin has an inventory of four tones, L(ow), H(igh), R(ising) and F(alling), six of their eight possible combinations trigger sandhi: LL->RL, RR->HR, FF->LF, FL->HL, RF->LF and RH->LH. Evidently, OCP is the trigger, applying at two different levels of the tone structure: the contour as a unit and the constituent tone features. This leaves two mysterious gaps as HH and FR do not undergo sandhi. In this paper, the mystery is solved through the recognition that Tianjin prosody is rightheaded and that tonal features contribute to prosodic weight.