What is always in front of you but can't be seen?

Once upon a time Dracula decided to carry some sort of a competition to see which is the finest bat to stand on his side. So all the bats were honored to take part. The rules were simple. Whichever bat drinks more blood, will be the winner? So the first bat goes and comes back after 10 minutes. Her mouth was full of blood. Dracula says: "Congratulations, how did you do that?" The bat said: "Do you see that tower? Behind it there is a house. I went in and sucked the blood of all the family". "Very good" said Dracula. The second bat goes and comes back after 5 minutes all her face covered in blood. Dracula astonished says, "How did you do that?" The bat replies " Do you see that tower? Behind it there is a school. I went in and drunk the blood of all the children". "Impressive" said Dracula. Now the third bat goes and comes back after three minutes literally covered in blood from top to toe. Dracula is stunned. "How on earth did you do that????" he asked. And the bat replies. "Do you see this tower?" Dracula replies with a yes. And the bat says "Well, I didn't".