Crooked bill hook and flat head hook.

1. Crooked-mouth hook: After catching an eel, the chance of the fish escaping is very small, because the barbs are large and biased to one side. After the eel eats the hook, there is basically no chance of escaping.

2. Flat-head hook: After the eel eats the hook, the eel's lower jaw will be stuck within this arc and will have barbs, which reduces the chance of the fish running away.