Another comment is that rats and mice, being the habitual gnawers that they are, take advantage of the block to gnaw on it, and the sharp edges make this more enticing to them for this activity. While we are still able to purchase 1 lb "cakes" that have plenty of sharp depressions in them for ease of breaking into smaller pieces for use, the more convenient form may be the Blox or Blocks that are already offered to you in small chunks that have the multiple sharp impressions in them. They also have the hole down the middle that makes it most likely that we will secure them within rodent stations using those horizontal and vertical bars. This is an added security against the bait somehow ending up outside, either dragged there by the rodent or bounced out by someone or something jarring the station. 

On that note, Dr. Corrigan reported some results of his testing of various stations and securing rods, and I thought the results might be interesting. First, in hot weather paraffin blocks are more likely to melt on horizontal rods than they are on vertical rods. Second, on black versus white stations placed outdoors in the sun, black stations were up to 60 degrees hotter inside than the ambient outside temperature, and sitting in the same place were 35 degrees hotter inside than white stations were. This significantly higher temperature could affect the consistency of that paraffin block. And, while we think of metal stations as probably oven-like inside, in fact their interior temperature was about the same as that of white or gray plastic stations.