> How else could *kaupo:jan- have
> developed? Into **kovUpiti?? It doesn't even look like a
> plausible Slavic word.
Why? Looks like a normal derivative of *(v)Upiti 'cry' with an
(intensifying or iterative) prefix *ko- ( ~ *ka-, of pronominal origin;
cf., eg., *kovIrzti 'weave', *kovIrtati 'spin', *kodUlbiti 'peck,
chisel', *kolupiti ~ *kolupati 'peel, pick', *konyrjati 'plunge').