Austrian state broadcaster ORF says the shell was on offer as a dummy. It says police had to clear a Vienna apartment house of its residents and put up road blocks after establishing that it was in fact a fully functioning explosive.
Thursday's report said police were called to examine the shell by its new owner shortly after she had exchanged two bottles of wine and a picture frame for it on an online swap site.
ORF said the shell's previous owner had used it as a door stopper.
The report says both women face unspecified criminal charges.
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