User blog comment:Broman178/Merlin's ability to sense magical objects./@comment-5350801-20120810200712/@comment-5102537-20120810204723

But when Merlin was able to sense the bracelet that Morgana gave to Arthur, why not a powerful necklace that reverses a powerful healing spell tenfold? Consuming the life force of a person or reversing a healing spell and killing the person seems to be equally powerful. Morgana, as the last High Priestess of The Triple Goddess, enchanted the necklace herself and it surely was not an every day item but a very powerful magical tool. Not to mention that Merlin's powers have been growing and he should now be able to sense even less powerful items.

If there are things that Merlin can't sense due to whatever reasons, there should be a mentioning and an explanation. The way it is handled now it seems to be just a plothole.