taking samples from barrels

[Newbie in CA]

I once saw someone taking samples from a whiskey barrel by using an old hand drill and drilling a hole directly into the head of the barrel. Once she had collected a small sample of whiskey in a glass as it poured out of the barrel, she stuck a slither of wood in the hole (looked like a toothpick) that she called a "spile" (I may have missheard). She said she could tell how old a barrel was by the number of spiles in each barrel head.

Anyone seen this practice before? What would the "spile" be made of - what wood?