1. A method of biometric sensing comprising: capturing at a biometric sensing element a time series of impressions of at least a portion of a fingerprint; receiving at a processor coupled to the biometric sensing element the time series of impressions of the at least the portion of the fingerprint; detecting in the time series a variation over time in the impressions of the at least the portion of the fingerprint; and determining a pulse of a mammal associated with the fingerprint based on the variation over time.