Bottlenecking

The original bottle contains a large number of three colors of marbles, blue and white in roughly equal numbers, and a few yellow. When the bottle is inverted, the narrow neck prevents all but a few marbles from passing into the smaller receptacle. By chance, no white marbles have passed through the bottleneck, and the proportion of yellow marbles is much greater than in the original bottle.

Compared with the original, the bottlenecking event has produced a sample that is (1) much smaller and (2) with a substantially different distribution.