Venipuncture question

Hey!

Had an interesting poke the other day and was wondering if some of the more experienced members could weigh in.

I was collecting a set of peripheral cultures from a hand vein which was quite palpable, during this poke, I initially got blood return followed by a high pitched squeaking (which I can only describe as being akin to writing on a white board with high velocity).

After the squeaking, blood flow ceased. At this point, I advanced the needle along the vein, to which I received blood flow (2-3 seconds) followed by squeaking and the loss of blood flow. I noticed that during this time, advancing and withdrawing the needle along the vein produced the same result (blood flow, squeaking, loss of blood flow)

I am curious what you think about this. I have my own contrived theory but I would like your input.

Thanks!