Borromean rings
... that the common depiction of the Borromean rings as three linked but pairwise-unlinked circles is an impossible object, because they cannot actually be circular?
... that the common depiction of the <b id="mwAQE"><a href="./Borromean_rings" id="mwAQI" rel="mw:WikiLink" title="Borromean rings">Borromean rings</a></b> as three linked but pairwise-unlinked circles <i id="mwAQM">(pictured)</i> is an <a href="./Impossible_object" id="mwAQQ" rel="mw:WikiLink" title="Impossible object">impossible object</a>, because they cannot actually be circular?