you can tell the user to enter commas after each word, and if you detect this you can do this
if(preg_match('/[,]+(,[,]+)+/', $word)){
$wordArray = explode(',',$word);
foreach($wordArray as $n=>$v){
$wordString .= "'%" . trim($v) . "%', ";
}
// clean end
$wordString = "(" . substr($wordString, 0, strlen($wordString)-2) . ")";
}
$whereClause = "Where Field IN " . $wordString;
//will produce "where Field IN ('%cow%', '%horse%', '%giraffe%')"
There are other ways of approaching this, any one of which could be very complex, generally you need to give some simple instructions to the client to use your algorithm.
Sam