The "Soviet joke" that I know, sanitized and ROT13'd:

Fbivrg fpvragvfgf qvfpbirerq gurer'f n qverpg areir pbaarpgvba orgjrra gur rlrf naq gur erpghz. Guvf jnf irevsvrq rkcrevzragnyyl ol bofreivat gung vafregvat na bowrpg vagb gur erpghz jvyy znxr gur fhowrpg pel, naq vafregvat n arrqyr vagb gur rlr jvyy znxr gur fhowrpg rkpergr.

I don't know the soviet version, but knowing a little Russian humour I will 100% bet that it is the same joke but with a person rather than a frog.