a small frog leaps--
h/t to my first commenter, who pointed me to a discussion of kaeru/kawazu. Kawazu may mean the itty-bitty Kajika frog (so cute!). Thus, "little" may make a necessary entry into the poem.
I have to admit, though, I'm not so into the indefinite articles--they're too amorphous, which distracts from the directness of the original, of its tender force.