Forty-five minutes later Ben showed up at my front door.

He had two plastic bags dangling from his bike handles. In one there were three cartons of milk. Full cartons.

In the other there were about forty lemons.

“The great thing about living in an apartment complex is that somebody always has what you need,” Ben said, carrying the bags into the house. “Especially when about nine out of ten people who live there are senior citizens. Senior citizens have the best supplies. They’re totally organized.”

“Why’d you get so much stuff?” I asked. “I mean, one lemon and one empty milk carton would have done it.”

“Yeah, I know,” Ben said. “Only, when Mrs. Markowitz heard that Mrs. Grimes was giving me a lemon, she swore she had an even better lemon, and Mr. Penderthal said he had the best lemons of all. It went on like that for about twenty minutes.”

“Well, all we need is one little lemon wedge,” I said.

Ben thought about this for a second. “Maybe we can donate the rest to charity,” he said.

We spent the next ten minutes drinking milk and eating cookies. Then I washed out the empty milk carton and sliced a lemon wedge.

“Step one,” I said, “is putting dust on the lemon.”

I swiped the lemon wedge on top of our fridge. It came back loaded with dust.

“Step two,” I said, “the lemon wedge goes in a plastic Baggie, and we add five drops of water.”

“And step three,” I said after I’d put the lemon wedge in the bag and Ben had used an eyedropper to drop five drops of water in with it, “is putting the Baggie in the milk carton and sealing the carton.”

“How long will it take the penicillin to grow?” Ben asked.

“A few days, I think,” I told him. “I’ll put the milk carton in the bathroom closet so it can get nice and steamy.”

Ben looked thoughtful. “You know, this science stuff is pretty cool. Not as cool as art, but almost.”

“I’m glad you think so,” I told him. “Because we’ve got a lot more work to do.”

There was mold to be made. Lots of mold.

Really, when you think about it, it was my kind of Friday night.

“Mold experiment number one,” I said, “bread mold. The world’s most common mold, some would say. All we need is a slice of bread, a plastic Baggie, and some water.”

“I get to do the water drops again!” Ben yelled.

“Okay,” I told him. “You’re good at that.”

Ben whooped. “All right!”

Sometimes it is ridiculously easy to make him happy.

The first trick was finding some bread in my house that wasn’t already moldy. Finally I noticed an unopened bag of white bread in a cabinet that looked relatively mold-free. I took out a slice, and Ben dribbled some water on it.

“Now we leave the bread exposed to the air for about thirty minutes, pop it in the Baggie, put it in a closet, and wait for the mold to start growing. We ought to see something in three or four days.”

“And then what do we do?” Ben asked.

“Just look at it,” I said. “Just admire the wonder and beauty that is mold.”

“So we don’t have to eat it or anything, right?”

“No way,” I said. “In fact, you’re not even supposed to ever open the bag again. Some people are allergic to mold spores, so you don’t want to let any out of the bag. Everything has to be destroyed.”

“That is so cool,” Ben said.

Next I found a nearly empty mayonnaise jar in the fridge. “We’ll clean this out and use it for our mold terrarium. We’ll put in four or five different kinds of food, spray on a little water, put on the lid, and wait for the fun to begin.”

Ben and I looked through the refrigerator and the cabinets and came up with one tomato slice, a piece of cheese, half a stale chocolate-covered doughnut, a handful of Cheerios, and a clump of macaroni. I turned the jar on its side and put the different foods inside. Ben added the water. “I can’t wait until all this mold starts growing,” he said. “It’s just going to be like this zoo of fungus.”

That’s when inspiration hit me. “Maybe we could jump-start it,” I said. “Give our mold experiments a steam bath to get them growing. Only, if we do it in my bathroom, Margaret will destroy everything.”

Ben frowned. “I’d say let’s do it at my place, but my mom would just scream and throw everything out.”

And that’s when I had inspiration number two. “But my mom’s not here. Her bathroom’s going to be empty until tomorrow night. We can put all the mold up there now, run a hot shower for thirty minutes, turn off the water, close up the doors, and let the steam do its magic. Who’ll know the difference?”

“Excellent idea!” Ben exclaimed.

It took us only a few minutes to transport all our mold experiments upstairs and get the steam bath going. Once my mom’s bathroom was nice and steamy, I shut off the water and shut the door behind us. “All right, then,” I said when we were back downstairs. “This is a good start. But the best part of our mold project is yet to come.”

“Better than spraying water on everything?” Ben asked.

“A hundred times better,” I told him. “A million billion times better.”

Ben’s eyes got wide. “What is it?”

“I think you better plan on spending the night,” I told him. “Because in the morning we’re going on a slime hunt.”