Difficult For Whom?

After her breakfast this morning, the munch monster wanted Jona to sit with her with Tiger in her hands while she did her jigsaw puzzle.

"It's so very difficult, Tiger!" she exclaimed as she deftly manouvred the pieces into place.

In the kitchen, I'm trying not to laugh my head off at her exclamation. At the same time, I'm wondering where she picked up that three syllable word. So I rattled off in my head the three syllable words she knows, with a few four syllable ones thrown in:

banana

apricot

strawberry

papaya

vegetable

crocodile

everybody

everywhere

beginning

difficult

disappear

watermelon

Note the recurring theme?