It's interesting, in words that Swahili has borrowed from other languages that end with a consonant, Swahili usually adds "i" (eg. baridi, lakini, intaneti) but if it ends with a "b", "m" or I guess also "p", there is usually a "u" added, probably because the lips are already closed so it's easier or "less conspicuous" to keep the lips rounded for the extra vowel (eg. kitabu, binadamu, jaribu).