As illfavor says, spenda and others also say... spoon especially says...

And as an experiment for myself... ranging this player might be difficult based on this line, but limping UTG as an 18/12, I'm giving him a range of 22+, AJs+, KTs+, AQo+. But also, I think we can rule out AA - QQ, as UTG would probably bet, not call those to open. Unless you're seeing something 'trappy' in his play.

So I'm thinking he may be on a KQs? Maybe AK with Ks, his line is really funky on the turn/river. To lead flop with nearly pot bet... then slow way down on the turn? Unless the spade scared him, but then to over-shove? I'm really thinking this line indicates Kxs to me... he really looks like he wants you to take the lead so he can get it in.

But I might be way off. Comments appreciated on all aspects of my casual player analysis.