  I raise some doubts concerning a protocol recently applied in an experiment
(Walborn et al, Nature) to measure entanglement. The protocol is much simpler
than other known entanglement-verification methods, but, I argue, needs
assumptions (namely that the state generated is known and pure) that are too
strong to be allowed and that are not justified in most experiments. An
extension of the protocol suggested in quant-ph/0605250 is much harder to
implement and still relies on assumptions not justified in
entanglement-verification protocols, as demonstrated by an explicit example.
