Modification of the critical curve near Tr by a nearby small perturber. This perturber is modeled as a spherical halo with surface mass density profile Σ ∝ r⁻¹ and a small core of 50 parsec. The halo is displaced 0.26″ south of Tr. With an enclosed mass of 1.38 × 10⁸ M_⊙ within this radius, this perturber is able to simultaneously explain the extreme magnification at Tr and the pair of knots between Tr and knot h of system 5. The HST image corresponds to the F814W band.