Matthew 16:7

ὅτι ἄρτους οὐκ ἐλάβομεν. ὅτι, probably not causal but recitativum i.e. used to introduce the words of the speaker. εἰ μὴ ἕνα ἄρτον οὐκ εἶχον (Mark). It is possible that Jesus may have employed figurative language even more than was usual with Eastern teachers; certainly this special metaphorical use of leaven was new. See Lightfoot, Hor. Hebr. ad loc. Again, the Pharisees had rules of their own as to what kind of leaven it was lawful to use, and what kind it was right to avoid. Hence it was not strange that the disciples should imagine that their Master was laying down similar rules for their guidance.