The act before your penis becomes erect due to factors such as seeing a woman and/or man that gets you horny. Normally, you get a warm, tingly feeling then your penis shoots up and your genitals start pumping up some sperm.
Tom: Hey, look at Becca there. Gosh, she has a smokin' hot bod.
Jerry: Yeah man! Yeah! She's giving me that Tingly Dingly!