They have no more than 2 incisors. These keep growing, and must be kept worn down by gnawing (eroding teeth by grinding them on something hard); this is the origin of the name, from the Latin "rodere", "to gnaw", and "dent", "tooth".
ð eɪ WORD_BOUNDARY h æ v WORD_BOUNDARY n oʊ m ɔ ɹ WORD_BOUNDARY ð ʌ n WORD_BOUNDARY t uː WORD_BOUNDARY ɪ n s aɪ z ə ɹ z WORD_BOUNDARY ð iː z WORD_BOUNDARY k iː p WORD_BOUNDARY ɡ ɹ oʊ ɪ ŋ WORD_BOUNDARY æ n d WORD_BOUNDARY m ʌ s t WORD_BOUNDARY b iː WORD_BOUNDARY k ɛ p t WORD_BOUNDARY w ɔ ɹ n WORD_BOUNDARY d aʊ n WORD_BOUNDARY b aɪ WORD_BOUNDARY n ɔ ɪ ŋ WORD_BOUNDARY ɪ ɹ oʊ d ɪ ŋ WORD_BOUNDARY t iː θ WORD_BOUNDARY b aɪ WORD_BOUNDARY ɡ ɹ aɪ n d ɪ ŋ WORD_BOUNDARY ð ɛ m WORD_BOUNDARY ɔ n WORD_BOUNDARY s ʌ m θ ɪ ŋ WORD_BOUNDARY h ɑ ɹ d WORD_BOUNDARY ð ɪ s WORD_BOUNDARY ɪ z WORD_BOUNDARY ð ɪ WORD_BOUNDARY ɔ ɹ ɪ d̠ʒ ɪ n WORD_BOUNDARY ʌ v ð ə WORD_BOUNDARY n eɪ m WORD_BOUNDARY f ɹ ʌ m ð ə WORD_BOUNDARY l æ t ɪ n WORD_BOUNDARY ɹ oʊ d ə ɹ WORD_BOUNDARY t ə WORD_BOUNDARY n ɔ WORD_BOUNDARY æ n d WORD_BOUNDARY d ɛ n t WORD_BOUNDARY t uː θ WORD_BOUNDARY