I've heard of this before but I believe it was rats and the supplier was getting lab surplus. Usually in the reptile industry when someone says 'lab rats' in regards to feeders, they are never the mice/rats that were *used* in the lab (since those could have unknown chemicals or toxins), they are the overage/extras that were not needed by the lab. Some feeder suppliers buy from multiple sources including those lab surplus to fill orders. Google search finds various threads from 2008 and 2011 discussing others that have found the same thing (slit throat) with their feeders but as for the why it was done, I cannot speculate and doesn't look like it was ever found out why it occurred. As others mentioned, it seems very inefficient.