When you reach the later half of the game you will find that the catapult will be particularly useful as it will enable you to shoot things such as frogs, eggs, and water balloons.
You will discover as you progress that certain objects you consume will enable you to do things such as shoot flames or fill you with water. Make a note of the effect these objects have on you so you can use it to help solve puzzles.
Wh-en you have swallowed the dwelling which the creature lives inside the stage will end, this means you need to make sure you have consumed everything else before you eat it.
At the start of the game your hole is small and you will only be able to eat things that fit inside. However as you consume things your hole will increase in size. This means you need to start off by eating the smallest things first and make your way up to the biggest.