There is a bronze trophy, Collar, for making Trico get his head stuck in every hole in the game. There are 15 holes. Some are mandatory, some are not.
We will point out the holes in this guide with a special formatting, making them easy to find and easily accessible from this compiled list, just click the descriptive
link below the hole.
As with other trophies, you don't have to do these all in a single playthrough. If you miss some, you can just pick up the ones you missed on a later playthrough.