Here's a few hints:
- He's got a bone stuck in a tooth. Perhaps he would be glad to help you pass if you helped him with his problem?
- Perhaps there is a way you could remove the bone from his tooth?
- You obviously have to come into his mouth somehow. But you're much bigger than his mouth!
- Giant is already bigger than you ... but could he become bigger?
- You have a spell that might not make the giant bigger... but it does make things smaller, doesn't it?
- ....just use the "shrink" spell and talk to the giant
If you have any more problems, feel free to ask!