An apparatus for use in fracturing wells includes a body defining and coupled to a wellhead of a well extending through a subsurface formation with the flow path being in communication with a wellbore of the well. The apparatus includes a flow meter in communication with the flow path and configured to measure a flow attribute of fluid from the wellbore along the flow path. The apparatus further includes a computing device communicatively coupled to the flow meter. The computing device is operable to receive a flow attribute measurement from the flow meter and to transmit an indicator in response to determining that the flow attribute measurement indicates interaction of a fracture in the subsurface formation with the well.