Translation:De kat raakt de hond aan.
Why is aan placed at the end of the sentence?
The full verb is "aanraken". You can check this for more information about separable verbs.
To complement Charlotte's link, you can read a (lenghty, but very thorough) explanation catered directly to Dutch learners starting here: http://www.dutchgrammar.com/en/?n=Verbs.Co01
Why is "aan" at the end?
It's a separable verb. See the links above :)
Just like voorlezen right? Now I know, thanks :)