Volume 43 of Marx and Engel's Collected Works covers their 1868 to 1870 correspondence.
Engels to Marx 10 April 1868
.......... Unfortunately, I have a death to announce to Tussy. The poor hedgehog ate a round hole in his blanket, put his head through it, and got so stuck in it that he was found strangled yesterday morning. Peace to his ashes, and BETTER LUCK TO THE NEXT ONE...........
The wedding was celebrated here with great festivity: the dogs had green collars, a TEA PARTY for 6 children, Lafargue's glass basin served as a punch-bowl, and the poor hedgehog was made drunk for the last time.Marx to Engels 11 April 1868
D'abord" the GENERAL CONDOLATIONS, and especially from Tussychen, about the departed RIGHT HONOURABLE HEDGEHOG.
It is a good thing that the opium prescription arrived today..........In summary, Friedrich Engels had a hard drinking pet (the Right Honourable Hedgehog) that accidentally strangled itself, almost certainly after a night out on the tiles.
My cup runneth over, to the extent that I am just leaving the opium thing dangling.