Contradiction in the Manciple's Prologue and Tale

Jeremy pointed out some striking contradictions in the Manciple's Prologue and Tale, but I would like to highlight one more. The moral of the Manciple's Tale is that silence is golden: the Manciple tells the pilgrims, "The firste vertu, sone, if thow wolt leere, / Is to restreine and kepe wel thy tongue; / Thus lerner children whan that they ben yonge" (332-4). Not only is it best to keep silent, but it is also best never to be the bearer of bad news, the mistake of the poor crow: "Beth war, and taketh kepe what that ye seye: / Ne telleth nevere no man in youre lif / How that another man hath dight his wif" (310-2). And one further variation on the same theme, he says, "keep wel thy tonge, and kepe thy freend" (319). The Manciple tells us one: to be silent, two: not to be the bearers of bad news, and three: silence has more friends. I found his message incredible ironic considering the Prologue to the Tale, in which the Manciple goes on a rather long and nasty rant about the Cook. The Manciple says to the Cook, in front of all the other pilgrims, "Hoold cloos thy mouth, man, by thy fader kin! / The devel of helle sette his foot therin! / Thy cursed breeth infecte wol us alle" (37-9). It's one thing to subtly hint towards a friend's bad breath by offering him a mint, but to say that that the devil himself has set foot in someone's mouth is quite harsh. He even says, "Fy, stinking swin, fy! Foule moot thee falle!" (40). He calls the Cook a swine, and then wishes ill upon him-- this hardly seems fair to the Cook, who is probably just suffering from a bad hangover. The Manciple's insults seem even more offensive after hearing his Tale, in which he touts silence and making friends by keeping silence. Perhaps the Manciple should learn to take his own advice!