Both.. I pop and probe. I pop babies and probe older snakes. I sometimes probe babies after a few meals and a couple sheds to double check if i had any doubts. Before selling or giving away any snake I always pop and probe to double check again if it's a youngster.
It is not uncommon for females to probe male on one side.
Males from juvie on up can hold it in which makes it difficult to pop.
Factoid: "There are no such things as Hogg Island or Columbian boas"