```python
def fill_between(entries: list, filler: str) -> list:
    """
    Fills in between two neighbouring entries in a list with a specified filler.
    
    Parameters:
    entries (list): The list of entries to be processed.
    filler (str): The filler to be placed between each entries.
    
    Returns:
    list: A list with the filler placed between each two neighbouring entries.
    """
    if_entries = []
    for i entry in entries:
        if len(profined_entries) < 2:
            if len(profined_entries) == 0:
                proficient_entries.append(entry)
            else:
                proficient_entries.append(entry)
                proficient_entries.append(filler)
        else:
            proficient_entries.append(entry)
    return proficient_entries
```