The weasel words in this case are "and so on." Four grains of wheat can make a heap. Put 3 on the bottom and one on top. If it's too windy to work where you are, slather them in honey. A sticky heap is still a heap.
Imagine you have a heap of sand. Now, if you remove a single grain of sand from a heap, it's still a heap, right? But if you remove every grain of sand, then eventually, you're left without any sand, which is definitely not a heap. So somewhere along the way, when removing individual grains of sand, the heap stopped being a heap. But where, exactly, did that happen?
(1) more than one vertical layer (the requirement for it to be a pile), and
(2) each grain not directly in contact with the ground being above a point on the ground within the triangle defined the points on the ground directly underneath three lower grains (distinguishing a heap from other piles).
(Of course, you may have a different definition of a heap, but if once you make concrete what you mean by a "heap", the problem is resolved. If you view heap as a fuzzy concept, then there is a continuous-valued fuzzy membership function, and there is no crisp point at which the collection stops, or starts, being a heap.)
Imagine you have a boat. Now take a piece off of it. Is it still a boat? How far can you go until it no longer holds the distinction of being a boat?
Yes, I know that submarines are colloquially known as (and are in fact) boats.
I believe that the quantity known as a 'heap' has an internet element of vagueness; that is it is not known the precise quantity of the heap. Or some specific property may be known but not all.
You might start by saying:
* This is a heap of wheat grain. -- As you know it is wheat the set includes any quantity larger than 0 (for nothing is nothing, though a container for heaps of wheat might be empty it's self).
* This is a heap of wheat grain weighing a kilogram. -- The number of grains, and possibly the volume and average grain sizes within the 'heap' are unknown, but now the heap has an additional bound, it weighs, within some range of error, a kilogram.
* A pile of 400 grains of wheat is exactly that. There is sufficient detail (an enumerate of the aggregate) that eliminates the vagueness implied by 'heap', though it would not be grammatically incorrect to introduce it thus:
This heap of wheat grain is comprised of 400 grains of wheat.
1. If X grains is not a heap, X+1 grains is not a heap. 2. 1 grain is not a heap.
You might disagree with 1 (or 2, though normally we'd disagree with one), but "and so on" isn't weaseling. It's plainly expressing the recursive applicability of 1.