Apparatus and methods are described for use with a bodily emission (26) of a subject that is disposed within a toilet bowl. While the bodily emission is disposed within the toilet bowl (23), light is received from the toilet bowl using one or more light sensors (60). Using a computer processor (44), one or more spectral components within the received light that are indicative of light absorption by a component of erythrocytes are detected, by analyzing the received light. In response thereto, the computer processor determines that there is a presence of blood within the bodily emission. The computer processor generates an output on an output device (32), at least partially in response thereto. Other applications are also described.