If you're still looking for that elusive ancestor, try revisiting the census for overlooked information. Or if you didn't find that ancestor the first time, perhaps the enumeration misheard the ancestor or the person giving the information. Look for the person using all those clues we've talked about. Use only the first initial, look for the parents, look using only the surname, etc. Don't forget that perhaps they lied, or the age may be way off, or the gender might be wrong.