The only thing I'll add first is this: Thatcher is a Southern Baptist bible scholar in the USA who's engaging with folkloristics (i.e., the cross-cultural study of folklore) as he tries to get at whether Jesus fits into a larger practice of riddling. Folkloristics, for Thatcher, just barely touches on Greek rhetorics (in other words, he hasn't recognized the discipline of rhetoric although folklorists have dabbled in it; and Thatcher has no idea how Aristotle - who worked through his own classifications for what's Poetic and what's Rhetoric - so despised riddles and riddling (and riddlish ambiguity and riddlish parables) as strange sophistry and as mere rhetoric, although such riddling ironically stumped Aristotle more than once); so there's much work yet to do (perhaps a dissertation topic for anyone working in biblical studies, historical Jesus work, historiography, rhetorics, feminisms, translation studies, and the like; if you want to do some publishable research with me on this, then just let me know).
Now, here's longish quotation of Thatcher (from page 47) that gives a bit of a definition to "riddle" and a bit of an explanation why so many so far have missed it:
The fact [is ...] that riddles don't necessarily stand out as "riddles" in obvious ways.... Riddles generate intentional ambiguity, and this ambiguity can, in turn, be harnessed to serve a variety of objectives (entertainment, teaching, test of wits, etc.). But those objectives do not depend on any particular style or form; as noted earlier, any statement of any shape or size can function as a riddle. Riddles come in a wide variety of forms in many cultures (like mine) simply because variety fosters ambiguity; they're more ambiguous if they don't always look or work the same way. For the same reason, riddles do not evidence a consistent content. Even within a single culture, there is usually no narrowly limited set of terms or themes to which they appeal again and again. As an example, the children's book to which I alluded in the preface, Bennett Cerf's Pop-Up Riddles, includes questions about ducks, bananas, kangaroos, eggs, 200-pound mice, and a host of other unrelated topics. Riddlers use this license to generate confusion; the more different things a riddle could potentially refer to, the better. Because the form and content of riddles are necessarily inconsistent, specimens of the genre are most easily identifiable by the way people use them and by the way that other people respond to them. But this makes the task of locating riddles as the sources for Jesus especially difficult, simply because we are not now in a position to ask Jesus or the Pharisees exactly what they were trying to do with their words on various occasions. As a result, riddles have fallen below the radar of the typical criteria utilized in historical Jesus research.What Thatcher is doing is fairly radical. It's Mary Daly-ish if you ask me. But if you yourself are anti-feminist-ish, please don't let that scare you off. Thatcher is really putting Jesus in a very large class of Jewish rhetors, including those who translate and who write some of the Jewish scriptures. This very large class also includes riddlers in Greek history (which linguistically, of course, intersects with Jewish scriptural histories in a grand way). But don't let that scare you off either if you're more Christian-ish, even more English Christian-ish of the Anglo, Australian, American, Canadian, New Zealand, Western-World varieties; maybe what Thatcher sees in Jesus can help with better Christian English Bible translation on difficult sayings such as “Ears to hear…” which might be seen (and translated) as a riddle marker.