1. That he's done with sex for the night.
Did you just have sex? Is it lying there, draped between his legs, passed out from exhaustion? Are you unable to rouse it from its slumber? Give it time to recharge. Refractory periods are standard, and most men need between 15 minutes to half an hour before they can go again.
2. That he had a bad day at work.
Is it not working as advertised? Maybe it won't get hard or ejaculate. It might have had a bad day at work. Maybe his boss yelled at him (at your boyfriend, not directly at your boyfriend's penis...that would be weird). But according to a study published in the Journal of Sexual Medicine, stress is a leading cause of erectile dysfunction among younger men.
3. That he totally wants to bone right now.
Is it hard? He's ready to go. Unless....
4. That he really, really has to go to the bathroom.
The only other reason it's hard is because its full of pee. Well, not literally. His bladder is full of pee, his penis is just maintaing an erection as a way to seal off all the urine. Like a penis dam.
5. That he had way too many tequila shots before he came over.
Maybe it's not stressed. He could just have had a little too much to drink.
6. That it's way too hot in your room.
Are his balls like a weird, fleshy pendulum, hanging extra low? That's the penis equivalent of a dog panting. Studies of temperature effects on the testes have long been documented, because balls are weird.
7. That you should exercise caution.
Are there any marks or bumps on it you don't recognize? Ask him (politely!) about it and cover it with a condom (as you always do, right?) before you touch. It could be a sign of an STD.
8. That you need to turn up the thermostat.
Is it small and cute and snuggling up next to the balls? That's because the room is way too cold. Testicles manage their temperature so they can keep sperm healthy, and penises close off their blood vessels and shrink when it's cold, so if his balls and penis appear to be spooning, get him another blanket.
9. That he just went to the gym.
Crotch sweat is the worst. That's because we've got tons of sweat glands down there, so things can get swampy in a hurry.
10. That he's circumcised.
Is it wearing a turtleneck made of skin? No? Then he's circumcised.
This article originally appeared on Cosmopolitan.com. Minor edits have been made by the Cosmo.ph editors.