of course it is a trap and not everyone reads chess books. thanx for posting this dkischess.

Umm... I know that "trap" posted by Kentering and it is a risk but probably small. 

1.e4 e5 2.Nf3 Nc6 3.Bc4 Nd4 4.Nxd4 exd4 5.c3:

5...c5 6.cxd4 cxd4 and white has a set of doubled-up pawns and is behind in developement.+-(I think)

5...Bc5?? 6.Qh5! threatening checkmate and the bishop on c5 6...Qe7 7.Bxf7 and the black queen can't take because he/she'll be losing by a pawn after the queen takes on c5 7...Kd8 or Kg8 and white is winning by a pawn and developement and I am 100% certain white wins a second pawn but I can't remember it right now.+-

5...dxc3 5.Nxc3 and white is up in developement but only a slight advantage.+=

...

thas what i mean while playing book move one should be well aware of it.

for ex. the time black plays Nd7 black is actually ready to sacrifice queen ....