Symmetries of a group G are encoded in the automorphism group Aut(G). "Hidden symmetries" are encoded in the abstract commensurator Comm(G). While many classes of finitely generated groups have reasonably well-understood commensurator --- for example, Comm(G) is typically a group of matrices with rational entries when G is arithmetic --- the abstract commensurator of a free group, Comm(F_2), is still somewhat mysterious. I will explain how Edgar A Bering IV and I fleshed out a topological perspective of commensurations that allowed us to show that every countable locally finite group is a subgroup of Comm(F_2).