The overall effect is that a molecule of HCN is added across the carbon-oxygen double bond. There are a number of tests that can be used to identify the presence of a carbonyl group in a compound. These rely on the oxidising nature of the various carbonyl compounds. These ions can be reduced by heating with an aldehyde. Again, ketones have no effect on this reagent.
Triiodomethane is a straw yellow solid, insoluble in water.