When speaking or even writing non formally, the "ne" are sometimes dropped. It's incorrect of course but perfectly understandable most of the time (dropping the "pas" instead is really weird but still understandable). My uninformed opinion is that this must just be a redundancy, which helps makes sure the negation is well heard, since missing it is generally catastrophic for the meaning as it generally means the opposite. Actually, in English negation can also add 2 words (do not), which also helps hearing it IMO. It also tends to be contacted. BTW I always have a problem with can vs can't, and often have to ask which one it is :)