Answer:
I'm not man's best friend, I'm their enemy, I can mark your end, yet you do not see me, I am very small, but very tough, If you have me, then you have it rough.
Of these things - I have two. One for me - and one for you. And when you ask about the price, I simply smile and nod twice.
Both old people and owls are said to be possessing this trait
What can be filled with empty hands?
What is it something that you always have but you always leave behind?
I have two eyes in the front and a lot of eyes on my tail
Difficult
Animal
Easy
Food
Funny
Kids
Logic
What am I?