  We explore the low-energy dynamics of 1/2-BPS heavy particles coupled to the
ABJM model via the Higgsing of M2-branes, with focus on physical understanding
of the recently discovered 1/2-BPS Wilson loop operators. The low-energy theory
of 1/2-BPS heavy particles turns out to have the U(N|N) supergauge symmetry,
which explains the novel structure of the 1/2-BPS Wilson loop operator as a
holonomy of a U(N|N) superconnection. We show that the supersymmetric
transformation of the Wilson loop operator can be identified as a fermionic
supergauge transformation, which leads to their invariance under half of the
supersymmetry. We also argue that 1/2-BPS Wilson loop operators appear as
1/2-BPS vortices with vorticity 1/k. Such a vortex can be naturally interpreted
as a membrane wrapping the Z_k cycle once, or type IIA fundamental string.
