So a few days ago when Boris was really restless and couldn't find anything to really hold his interest, I spread out the mat and poured some lentils into a bowl. I got some metal measuring cups out and let Boris go wild.
He really enjoyed them again, scooping the lentils from one cup to another, spreading them around, running his fingers through them, stirring them, pouring them, sprinkling them through his fingers, throwing them about. I didn't mind that the lentils went EVERYWHERE because he was so engaged with the activity. It came to an end when he took a scoop full of lentils outside and....started eating them.
We played together with the lentils for a good 20 minutes and Boris even had a bit of fun banging to cups together and watching himself do it in the mirror. It did take a long time to clear them up after, and there was substantially less in the pack after I had to hoover a load up that had breached the perimeter of the mat! They got everywhere, stuck to my feet and I even found one sitting on my fat pregnant tummy when I was undressing for bed! Made me chuckle to myself. But it was definitely worth it because he had a great time and the activity somehow really soothed him; enough for him to be able to entertain himself for some time afterwards. A highly recommended activity which I think has further potential as Boris gets older, in terms of weighing and measuring, and in craft activities.