Kids as Leeches

Why is it that your toddler can ignore you when they have something to do but as soon as mom gets on the phone or sits down at the computer, they become little leeches, crawling all over you and demanding you pay attention to them very loudly (and I do mean LOUDLY)?

My two-year-old is a little blond leech who can SCREECH if she notices my attention go elsewhere. When I have another mom on the other end of the phone, they understand. They've been through it. When I have somebody on the other end of the line that doesn't have kids, they can't get off the phone fast enough.

I guess all that loud, annoying screeching and pawing at you is only behavior the toddler's mother (or father) could love.