Binds beta-galactoside and lactose. Strong inducer of T-cell apoptosis (PubMed:10527825, PubMed:19497882). Has hemagglutinating activity towards chicken erythrocytes (PubMed:29343868). Acts as an activator of ferroptosis: secreted by ferroptotic cells and acts by reducing localization of SLC7A11 at the plasma membrane (PubMed:40246981). {ECO:0000269|PubMed:10527825, ECO:0000269|PubMed:19497882, ECO:0000269|PubMed:29343868, ECO:0000269|PubMed:40246981}. This is the function of LGALS13 (galectin 13, ENSG00000105198).