Running a little warm during video playback

[mikeyv2009]

So I noticed that when watching a ten minute YouTube video over wifi my phone got a little warm on the back.. By no means was it hot or even really "toasty", just a little warm... Is this normal or should I be alarmed and send it back for a replacement?

 

[Suzi_Derkins]

My phone gets toasty, but I'm not too worried about it.