My last question was answered so quickly and so successfully, I'm going to present another, which I fear may not be as easy to answer. It is one of my holy grails...
Somewhere back in the '70s (between 1970-and 1977, and probably closest to 1974-1975 +/-2 years) I read a short-short SF/Horror story in one of the little free magazines that we sometimes received in school from Scholastic and possibly other sources.
One day a friend showed me a story in their copy of one of these little magazines (it was more or less digest sized) that I had missed because I was out sick (so this was probably in the winter? it explains why I never had my own copy though). The narrator of the story is a child attending another child's birthday party in the future (at least in the future as perceived from the mid-'70s), and bringing a special gift made in the lab in which his/her father worked (I can't remember with any certainty the gender of either the narrator or the recipient of the gift, though I think the recipient might have been a girl).
The gift is a little box or cube, and a string or cord extends out of a hole on one side of the box. When the recipient of the gift pulls on the string, the string pulls back. A delightful tug-of-war ensues, until suddenly whatever is on the other side of the string pulls so hard the birthday girl(?) is drawn into the hole and disappears inside the box. Possibly followed by screams and/or crunching/eating sounds...
The climactic line of the story was something close to "I forgot the monster on the other side of the nowhere-hole could pull back."
I also distinctly remember a rather spoilery illustration of a monster accompanying the story. The image (which appears in blue ink in my memory) was a frontal depiction of a ragged and vicious-looking humanoid monster with a fibrous cord extending from the tip of one of its claws.
I have searched in vain for this story for 40 years, and will be genuinely indebted to anyone who can ID it and/or help me locate a copy. THANK YOU!
After I posted this query here, I shared a version on my Facebook page as well, and several friends stated that they too remembered this story. One of them was able to add the following details, all of which fit my memory:
"The scientist/parent was the child's mother. After a few back and forth pulls on the "string" the birthday boy made the mistake of wrapping the string around his hand, then yanking really hard. All the party attendees heard his screams after the birthday boy was pulled into the box. The child [who brought the gift] was subsequently shunned by the other neighborhood parents/children after the incident. In retrospect, an awful story to give to a 10 or 11-year old!"
Some of the responses narrow the likely publication date down to somewhere between 1973-1975, although one or two of my friends were fairly certain they read it in a later anthology, possibly in the '80s, so there may have been at least one reprint.
The original publication was in one of the free magazines like Weekly Reader or "READ: The Magazine for Reading and English." The latter seems most likely given some of the examples I have been able to find online. The story was DEFINITELY NOT in Bananas or Dynamite. These were fancier, glossier publications, and both started a little later. [NOTE: I spent my entire day today (17.Jan.2018) going through microfilm archives of READ Magazine from Sept. 1971-May 1977. Didn't find it. So it must have been in Weekly Reader or some even more ephemeral publication.]