As far as I understand, CV-QKD (also here) uses coherent states to send a key, that is encoded in amplitude and phase quadratures. When someone tries to eavesdrop, this will introduce an error and therefore the eavesdropper is detected. I think I can see that an intercept/resend attack of any kind would introduce such an error. What I do not understand, however:
How is the error introduced if and eavesdropper just taps a few of the photons?