The shears mechanism, underlying the rotational-like behavior observed in the M1 bands in neutron-deficient Pb isotopes, is interpreted as a consequence of a residual interaction between the proton and neutron blades. By deriving the angle {theta} between the proton and neutron spin vectors {rvec j}{sub {pi}} and {rvec j}{sub {nu}} in the {sup 198,199}Pb bands, it is shown that the main ingredient of this effective force can be described by a P{sub 2}({theta}) term with a strength of 400{endash}600 keV. Such an interaction can be mediated through the core by particle-vibration coupling, and qualitative agreement with experimental estimates may indicate the possible role of this coupling in the appearance of shears bands. {copyright} {ital 1998} {ital The American Physical Society}