utrisque: found in Catullus in the plural only here and in v. 6; and in general the plural is much more common in prose than in poetry.
 erudituli: Caesar was not only a historian, but a grammarian (Suet. Iul. 56; Cic. Brut. 72.253) and a poet (Suet. l.c.; Tac. Dial. 21; Plin. Ep. 5.3.5). On Mamurra's attempts at poetry see Catul. 105.1ff.
 rivales socii: here it appears better to take rivales in its original implication of not unfriendly rivalry, the two friends vying with each other in the number of their mistresses; v. 9 thus completes v. 8; cf. Tac. Hist. 1.13 “[Otho erat] gratus Neroni aemulatione luxus” .