Critter Crunch

It is not possible to clear every puzzle level with moves to spare, in many cases you need all the moves available to clear the level. The earliest level where it is possible is puzzle level 10, though the simplest one is puzzle level 12. I also found that levels 15, 17, and 22 can be completed with spare moves, and probably many more of the higher numbered ones.

To achieve this on puzzle 12, just take one fly from the leftmost column and put it in the middle column, then take the remaining fly from the leftmost column and feed it to the green critter in the rightmost column, triggering a food chain and combo that will clear the level with one move to spare.