Not sure if this always works..but has at leas 7/10 times for me...

If you circle your pointer around the eyes of the mask at the bottom of the screen, his eyes light up. if you keep them brightly lit for about 25 seconds, and then go searching around the island, it pops you up a collectable. either something for your collection, or a mushroom. try, if it works for you, let me know here....