Lenny being this dumb makes no sense

Not a lot of this movie makes sense (especially Dodd's sudden docile, compliant and non-inquisitive behaviour (let Lenny sleep without trying to get out of the predicament or standing up in the closet, kicking the closet doors, etc. etc., Jaguar in the parking lot with NO ONE even being curious about it, etc.)..

..so here's yet another thing that makes no sense.

Lenny is supposed to be a smart guy. Evil, psychotic, but smart. However, what kind of sense does it make that he's ready to touch Natalie's face, PUNCH Natalie, but... not rob her? I mean, he'll beat her up but not touch her purse to find a pen? Not tie HER up like he did Dodd (gender equality for ya), and control the situation that way, not simply STOP her from leaving until everything gets cleared up..?

Why does he let her leave, move, do whatever she wants and hoard all the pens? No red flags go up when he sees her taking every pen? Why DOESN'T Lenny have his own darn pen anyway? He seems to intuitively know he needs to write a lot, so shouldn't he have at some point acquired a couple of pens? I know, the clothes, etc., but come on.

Somehow weirdly and SUPER conveniently, Teddy KNOWS to give him a pen, because Teddy somehow knows he doesn't have any pens, no one could've given him a pen, Natalie hid all her pens and so on. Why would he even think Lenny doesn't have a pen? Somehow he instantly offers his pen so the movie can happen, sigh. I hate this kind of convenience in movies.

In any case, shouldn't Lenny be smarter than just letting Natalie leave after he punched her? Shouldn't Lenny go THROUGH HER PURSE and stuff and tie her up and control the situation and find out what's going on? He does SO much to Dodd with much less motive, this beach (sic) insulted his beloved wife and he STILL doesn't do as much to her as he does to Dodd?

Lenny couldn't be this stupid, but the movie has to happen, so suddenly he's a real dumbo that doesn't think to stop Natalie from leaving and going through her purse, then writing himself what happened after tying her up and so on.

It's sad what happens to characters when movie has to happen a certain way, they can't be intelligent anymore... but it makes no sense.