In the third person singular (il, elle, on) it can happen that two vowels meet, the one with which the pronoun starts and one the verb ends in. If this is the case then a t is put inbetween.

no problem    
Elle vend sa voiture. => Vend-elle sa voiture?
She sells her car. => Does she sell her car?  
Il est content. => Est-il content?
He is content.=> Is he content?  
Elle parle italien. => Parle-t-elle italien?
She speaks Italian. => Does she speak Italian?  
Il s' achète une nouvelle voiture. => S' achète-t-il une nouvelle voiture?
He buys a new car. => Does he buy a new car?  
Il ne pense qu' à lui-même. => Ne pense-t-il qu' à lui-même?
He only thinks about himself. Does he think only about himself?  

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