on side feathers , he refer since they know .
(ROOT_0 (S_0 (ATS_3 (ATS_1 (ATS_2 (PP_2 (IN_0 on) (NP_3 (NN_0 side) (NNS_1 feathers))) (COMMA_0 ,)) (NP_0 (PRP_1 he))) (VP_3 (VBP_0 refer) (SBAR_0 (IN_2 since) (S_1 (NP_0 (PRP_1 they)) (VP_5 (VBP_0 know)))))) (DOT_0 .)))