Excel formula to return all matching strings within a cell

I have one column that looks like this:

    screws
    nails and screws
    nails
    screws, nails

I'm trying to create a new column containing only given keywords, so the output would look like this:

    screws
    nails screws
    nails
    screws nails

I've been using =IF(SEARCH("nails",A1,1),"nails",IF(SEARCH("screws",A1,1),"screws","")) but of course if the first statement is true it doesn't bother searching for the next.