I walked in on my 8 year old son masturbating and I don’t know what to do

I (36f) was washing dishes in the kitchen, as I was looking out the window I notice my son (8m) sitting on the couch, touching his front. I didn’t think anything of it as he usually does this when he is scared or nervous. I kept looking and noticed his hand was moving. I immediately stopped looking as I felt bad and I didn’t wanna intrude on my son. I haven’t mentioned anything to him about it. I’m worried because I don’t know if this is normal behavior for an 8 year old. He’s never mentioned anything about this. What should I do in this situation. He’s my only child and I don’t know what boys do at this age.<br><br>UPDATE: I spoke to my son and he didn’t know there was a problem with this. After speaking to him he understood that some things are private so you should do them in your room. He thanked me for speaking to him and telling him it was ok and it’s nothing to be ashamed of.