We provide a characterisation of strong bisimilarity in a fragment of CCS that contains only prefix, parallel composition, synchronisation, and a limited form of replication. The characterisation is not an axiomatisation, but is instead presented as a rewriting system. Our approach is extended to derive a new congruence result in the pi-calculus: congruence holds in the sub-calculus that does not include restriction nor sum, and features a limited form of replication. Whether this property holds with unrestricted replication remains open.