Here's how it functions:
* Adverb: It modifies the verb "open," providing information about how the action should be performed.
* Parenthetical: It's set off by parentheses, which indicates that it's a non-essential element of the sentence. The sentence would still be grammatically correct without it.
* Function: It emphasizes the importance of opening the crate with caution. It adds a layer of instruction or advice to the main command.
Therefore, the function of "carefully" in parentheses is to emphasize the importance of performing the action with caution and to provide extra instruction to the listener.