You'd be dumber if you can't even understand the actual context. Kindaichi specifically set up a trap for Izawa, whom he knows is the true culprit, by making him think Kindaichi will point the finger at Hoshiko, a scenario in which case suicide by poison would make sense for her to do. Thus...
Not obviously so, but remember: those metal pieces were found in a vacuum cleaner bag, among the broken glass that was dropped in front of Shizuki's room door. Kindaichi himself even said his fingerprints are bound to be on them.
So, to summarize:
Two thin, black metal pieces, the color of...
"Because you're both just as guilty for even considering Tsukishima-kun's nonsense"
...Except the video clearly implies neither seemed to agree with his idea.