  Linear defect modes in one-dimensional photonic lattices are studied
theoretically. For negative (repulsive) defects, various localized defect modes
are found. The strongest confinement of the defect modes appear when the
lattice intensity at the defect site is {\em non-zero} rather than zero. When
launched at small angles into such a defect site of the lattice, a Gaussian
beam can be trapped and undergo snake oscillations under appropriate
conditions.
