Use it this way:
Options +FollowSymLinks
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^([^.]+?)/?$ index.php?p=cats&s=$1 [L,QSA]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.+?)\.html$ index.php?p=prod-detail&p=$1 [L,QSA]