For the symbiote to filter cyanide, it must anticipate cyanide. What lifeform does? Anyway, something'd need to combine with it, and some source said sulphur. Hmm, that's interesting. Iron is in the same group as osmium and naquada. So the naquada in the bloodstream could combine to the cyanide. But what does it do with it... It needs to be electrolysed and combined with oxygen, spare oxygen that's still in the blood, lest the naquada cyanide keep accumulating. Also, for a double threat, one can blow CO through the shield with the C2N2. CO can be produced from water gas; that is, passing steam over red hot coals. (H2 comes out too.) C2N2 is produced doing the same but with the presence of ammonia. The CO will remove whatever oxygen's left in the bloodstream. The symbiote can't win!