But at this point Jesus leaves off use of φαγεῖν to adopt a more provocative tone: he who eats (τρώγων) his body and drinks his blood will have eternal life. Now τρώγων, a participle of τρώγω, in a sense bears more resemblance to fressen: the Middle LSJ gives “gnaw, nibble, munch”. And this, the Catholic exegete (e.g. Robert Barron) will tell you, would have shocked the listener. Unlike φαγεῖν, τρώγω, which calls to mind the animal act of eating, is much harder to dismiss as figurative speech. This passage begins with the debate over how Jesus is supposed to give us his flesh/body (σάρκα) to eat. How is this possible? Jesus does not answer directly, but assures them, in effect, that they are to really, physically eat his real, physical body. And, as if they had missed it the first time, Jesus hammers it in three more uses of τρώγων.
But, interestingly, there’s enough of a difference between τρώγω and fresse to preclude any German translators that I know of from using fressen to mark the variation in Jesus’ speech. I suppose this is because fressen above all connotes the abandon with which animals devour their food. And if anything, what Jesus had in mind was a civil and communal meal. Still the animal associations of τρώγων, to meditate on the image a moment, recall the manger that Jesus, who now calls himself the bread of life, was first placed in a town notably called Bethlehem - the House of Bread. I don't know how long it took me as kid to figure out that a manger is something animals eat out of, but this is doubtlessly more than a fact Luke picked out to indicate the meager circumstances attending the birth of Jesus. Just as mention of Bethlehem was more than a means to reconcile the messianic birth with the prophecy of Malachi. Just as, for that matter, calling attention to Jesus' swaddling clothes foreshadows the wrappings worn by Lazarus and those left neatly folded by Jesus himself before leaving the tomb.
On the patristic reading, the entire Bible is steeped in eucharistic imagery, and when it comes down to it, expressions of the Real Presence of the table-pounding variety such as the one above. Another, just for fun: the emphatic use of ἐστιν (is) in Matthew 26:26, Mark 14:22, Luke 22:19 (Τοῦτό ἐστιν τὸ σῶμά μου) and 1 Corinthians 11:24 (Τοῦτό μού ἐστιν τὸ σῶμα τὸ ὑπὲρ ὑμῶν). In Greek the appropriate form of "to be" is very often omitted.