Anybody any idea quite interesting leaf

i would worry about leaf colour, not about form.

Fun stuff. Maybe it was damaged a bit and grew in like this. Kinda like a split/snake tongue body mod some people get done to them. looks fun. Noting to worry about though IMO It does look like its also has a bit of Two-Toned Leaves as well. My one plant outdoor also did this. but it was a bit more pronounced. Just a common mutation, https://bucket.growdiaries.com/static/post/photo/31185/9747601_c36c15d5a2aaaea1c25981e6cdd6f9a0_big.jpg One of the leaves in the back has a bit of spotting and is reminiscent of calcium deficiency. Ensure your feed is complete. and maybe next time adding in a bit more perlite into the medium could help.