The spread on the Bristol-Myers Celgene deal has been closing rapidly and is even negative when ascribing no value to the contingent value right or CVR.
This is happening because the transaction could close relatively soon (I put the closing date ~27 days from here).
If the deal closes, Celgene shareholders receive 1 contingent value right per share.
Another reason may be that the contingent value right has been growing in value since it was first offered.
The value of the contingent value right is hard to estimate, but my baseline estimates indicate it could be worth over $6.