During "Pylon Express" Holly arrives on Earth, but decides not to leave the pylon because she doesn't want to leave Rick and Will behind. She arrives in the middle of a park where people are playing frizbee yet no one looks at her. If something like that appeared while I was playing frizbee I'd stop and acknowledge it. I have some theories why they didn't. It could be:
1.) The pylon is invisible to them.
2.) It wasn't actually Earth, only a place disguised as Earth to lure Holly out.
3.) They were so absorbed in their frizbee game they didn't notice her.
Any other opinions? Am I over-analyzing this?