How much sand can an engine apbsorb?

[crazypete]

I know this is a stupid question: the answer is none, but here is the situation:

I was taking off the lower intake and, amongst other things, I found walnut shells, leaves, sand, that nice engine gunk and a lollipop stem sitting on my lower intake. So I scooped then brushed then used a vacuum cleaner then compressed air but when I finally pulled the intake, some sand trapped between the cylinder heads and the intake fell onto the rollers and a bit into the intake ports. I wiped and vacuumed 98% of this up. Should I be overly concerned about a few wayward grains of sand? Will the engine grind them up or it it going to seize immediatley?