Commentary for Exodus 5:8

ואת מתכנת הלבנים means the total number of bricks which each made per day when straw was being supplied to them — that total you shall impose upon them now also, in order that the service may be hard upon them.

מתכנת, the quota.כי נרפים הם, they are therefore able to make more of these bricks daily.

כי נרפים הם, "for they are lazy!" Who had ever suggested that the idea to sacrifice to their G'd originated in the relatively light burden of work that Pharaoh had imposed on the Israelites up until then? Perhaps what Pharaoh meant was that the Israelites felt that now that Moses had arrived their lot would become easier and that therefore they wanted to thank their G'd for that by offering up thanksgiving sacrifices so that He would cancel out the servitude altogether. Pharaoh countered this euphoria by making the workload heavier so that they would not even entertain any idea of their servitude being near an end, i.e. those lies that Moses had fed them.