Catullus knows that a lot of the time, witty remarks and spiteful words are more powerful than physical fighting, and so this is why people never hear about Catullus being in a fistfight, but often hear about his invectives, like Catullus 37 and 39. Catullus wishes to cut deeply and permanently, to leave scars that can't be seen by the eye. And not only does he do this to the face of those he dislikes, but he writes of it, so posterity knows of these disgraceful people. Catullus wishes to inflict emotional pain, not physical pain, to really hurt those he dislikes. He does this because he knows this will do longer lasting, more widespread damage, not only to the person, but to their reputation.
In Catullus 37 and 39, he displays his anger towards a group of men gloating about their sexual exploits. Catullus does not do this by calling them everyday names, but finds much more creative ways to insult them. In Catullus 37, he does this in multiple ways, one being that he tells the group of men to sit in a line and he will have all of them blow him (Cat 37.6-8). He then threatens to draw penises all over their tavern (Cat 37.9-10), and criticizes the men for gloating about sleeping with his beloved Lesbia. In Catullus 39, he singles out Egnatius, who was a part of the group of men from 37, and further tears him apart, saying that "Whatever is going on, wherever he is, whatever may happen, he grins," even if the occasion is in court or at a funeral (Cat 39.6-7). Catullus then states that the higher the polish on Egnatius' teeth, the higher it shows that Egnatius drinks his own piss (Cat 39.20-21).
Both 37 and 39 use the same meter, and both are invectives of Catullus. They are both meant to attack, insult, and degrade the subjects of the poem. Both also start out by addressing the recipient(s) of the insults, whether it be the lecherous tavern and its companions (Cat 37.1) or Egnatius and his bright teeth (Cat 39.1). They both also end by stating that Egnatius drinks his own "urina" (Cat 37.20) or "loti" (Cat 39.21). In 39, Catullus repeatedly uses "aut" (Cat 39.10-14) to show a stream of consciousness, because he is building up to the end, getting more and more intense.
Catullus artfully uses connotations in his poetry to further his point, and uses them to add greater bite to his invectives. The word that stands out the most in both 37 and 39 is urine. It only appears in line 20 of 37, and in line 21 of 39. Urine implies all of the dirty, disgusting, unclean, things not worthy of use, and yet Egnatius is shown to use it daily to polish his teeth. This is just another way Catullus personally insults Egnatius.
Catullus picks some interesting symbols in his poems, and in 37 and 39, his chief symbol is Egnatius himself (Cat 37.17 + Cat 39.1). Egnatius represents all the terrible, lowly, gossiping lowlifes who find pleasure in others' failures. Catullus is not only attacking Egnatius, then, but what Egnatius represents, knowing that his words will do more damage than simple brawling. The Celtiberians (Cat 37.18 + Cat 39.17) are also a symbol, representing old, barbaric ways, and so Catullus also insults Egnatius' people. Catullus will not stop in his assault of Egnatius, degrading all that he comes from, is, and represents.
Catullus 37 only alludes to the Celtiberians and Spain (Cat 37.18+20, respectively). Catullus 39 alludes to the Sabines, Tibur, the Etruscans, Umbria, Lanuvium, and the Celtiberians (Cat 39.10+10+11+11+12+17). Catullus repeatedly alludes to more primitive, less developed peoples to equate to Egnatius. Catullus relentlessly assails Egnatius and his background, making his onslaught as personal as possible. Catullus will not let up in trying to hurt Egnatius on the inside, and in these intense actions shows he cares a lot more about hurting internally than externally.
Catullus uses the same meter in both poems, and starts and ends them in a similar fashion. There are obviously strong connections between these invectives, because Catullus wishes for everyone to know of disgraceful Egnatius. Catullus seems to be much more emotional in his own attacks in 37. In contrast, he seems to be much more rational in his approach in poem 39. Catullus is showing that in any state of mind, Egnatius is not a nice guy.
Catullus unleashes a volley of insults in such aggression that his passion for language and its power is clear. Catullus clearly realizes that his talent is to hate and insult verbally, all the while knowing this will have a greater effect on Egnatius. Catullus' belligerence in his poetry is his substitute for an physical confrontation, because Catullus is far more cunning than that. Catullus wishes to cut deep and permanent, and this offensive launched against Egnatius in his poetry proves it. And one last piece of evidence to prove this: the full damage is still not done, because Catullus' attacks on Egnatius have lived on for generations, and will live on for more, so that Egnatius will be ridiculed and laughed at even farther into the future.