Having just discovered that Joseph Haydn's "Frog" quartet (Hoboken III/49, published as Opus 50, Number 6) is not included in the Brilliant Classics Haydn Edition, I find myself returning to the problem of trying to explain its name, which I first encountered this past March. In my Examiner.com review of the Prazak Quartet, I had the following to say about this name:
In his monumental Haydn: Chronicle and Works, H. C. Robbins Landon never explains the "Frog" sobriquet. He cites a bouncing cello motif in the first movement; but he compares it to "a child's skipping rope." To my ear the trochaic (accented-unaccented) rhythm of the Menuetto was Haydn's ranarian inspiration.
Now that the Haydn Edition has been inspiring me to pursue various resources about all that music, I came up with an alternative explanation from, of all places, Wikipedia. This was not in the Haydn entry but in the one for bariolage. Here is the quick definition in the first sentence:
The bowed instrument musical technique known as bariolage involves quick alternation between a static note and changing notes, that form a melody either above or below the static note.
This is then elaborated further in a subsequent paragraph:
Bariolage can also mean a repeated alternation between the same note on different strings, usually an open string and the same note fingered on the adjacent lower string. Joseph Haydn used this effect in the minuet of his Symphony No. 28, in the finale of the "Farewell" Symphony, No. 45, and throughout the finale of his String Quartet Op. 50, No. 6. It is the unison bariolage passages that give this quartet its nickname The Frog.
Clicking on the "discussion" tab for this entry, I discovered that this extended interpretation of bariolage probably came from a user identified as ILike2BeAnonymous; but this latter interpretation is basically consistent with the definition of bariolage given by David D. Boyden and Peter Walls in Grove Music Online. This being the case, it would appear that "Haydn's ranarian inspiration" had more to do with croaking, rather than with the connotation of leaping that I had been seeking!